FAQ/Glossary

A variety of chrysoberyl. A stone with a color-changing property: green in natural light, red in artificial light. Mohs hardness: 8.5.

A fired crucible made primarily of alumina (aluminum oxide). Used for melting metals with high melting points, such as platinum.

A vitreous stone of the quartz family, showing pale purple to deep purple colors. Mohs hardness: 7.

A quartz combining the purple of amethyst and the yellow of citrine. Also called bi-color quartz. Mohs hardness: 7.

A talisman or protective charm of gemstones or jewelry, believed to protect the wearer from disasters or demons.

A transparent stone showing pale blue to blue. A variety of beryl with a vitreous luster. Most stones undergo heat treatment to improve color. March birthstone. Mohs hardness: 7.5.

Arc welding performed within argon gas jetted from the electrode torch. Blocks out air to prevent oxidation. Used for welding silver jump rings, etc.

A chain made of continuously linked round rings. There are many varieties depending on ring size, wire shape, and assembly method.

The eaves-shaped undercut carved into the base metal to inlay a piece during inlaying, as well as the burrs produced when carving that undercut.

A gold alloy where the silver-to-copper ratio of the alloying metal is 8:2 or higher (more silver than copper). Called green gold due to its strong greenish tint, though there is no strict definition of the ratio. Also called white alloy.

An abrasive made by solidifying chromium oxide powder and a small amount of calcined alumina with grease like stearic acid. Used by applying to a buffing cloth to produce a high luster on metals. Collectively called Aoko (green powder), including solid and powder forms.

A setting style where the base metal surrounding the engraved setting area is rounded into bead-like shapes using a milgrain (nanako) chisel, creating the illusion of being paved with beads.

A method of quenching where the metal is heated to a suitable temperature and then rapidly cooled by immersion in oil. Often done when making chisels from red turnip steel.

A gold alloy where the silver-to-copper ratio of the alloying metal is 2:8 or higher (more copper than silver). Called red gold due to its strong reddish tint, though there is no strict definition of the ratio. Also called red alloy.

An abrasive made by solidifying ferric oxide (rouge / bengara) powder with grease. Used for finishing metals. Collectively called Akako (red powder), including solid and powder forms.

The file with the coarsest teeth. Often used for grinding down sprues on items fresh from casting.

Roughly filing something into shape using a coarse or medium file.

A general term for applying a matte surface finish using roughing chisels, roughing hammers, etc.

A file with the finest teeth. Often used before scraping (kisage).

A bluish-white lustrous metal. Alloys with copper (brass) have wide applications. Sometimes added in small amounts to improve fluidity during casting, but it can vaporize into soot and damage the casting furnace. Also used as an additive to lower the melting point and improve the flow of solder. Boiling point: 907℃. Melting point: 419.58℃.

The act of pouring molten metal into a mold during the casting process. Also called pouring (chuyu).

The loss of material quantity during casting. Includes vaporization during melting and penetration into the crucible or mold.

Shrinkage during casting. Includes shrinkage upon solidification and shrinkage down to room temperature after solidification. Products are designed accounting for this shrinkage.

The surface of an item immediately after casting. If this is smooth and beautiful, subsequent processes will go smoothly.

The measured weight of a gemstone. If a product has multiple types of gems, they may be stamped separately. Unit is ct (carat). Many overseas products do not have weight stamps, as there is no law requiring it.

The mother oyster of freshwater pearls. A large bivalve living only in parts of the Yodogawa river system, mainly Lake Biwa. China cultivates freshwater pearls using a related species.

A soft wax injected into rubber molds to form wax patterns. Also called soft wax. Colors like yellow-green, blue, and pink vary by use.

A general term for gemstones and jewelry with an incised (sunken) carving design, in contrast to cameos which are carved in relief. Used not only on stones like agate but also on the faces of signet rings.

The mold into which molten metal is poured during casting. Mainly refers to plaster molds. In lost-wax casting, it is the state where the investment material (plaster) in the flask has a cavity left by the wax tree.

Cracks or collapse occurring in the mold during dewaxing or firing. Causes vary, such as poor slurry mixing, rapid wax expansion, or extremely thin/narrow wax patterns.

Sulfurizing degreased silver 925 using sulfur liquid to turn it gray to black. Leaving some parts unpolished creates a contrast between mirrored and black areas. Sulfur reacts with copper, so it does not affect platinum, pure gold, or pure silver. Copper sulfate solution can also be used.

A tool consisting of a thin saw blade attached to a frame. Used to cut out metal plates. There are various types of blades by shape and thickness, used depending on the purpose.

A ring originally used as a seal. Often engraved with names or crests, or set with intaglios. Today, most are used as fashion items rather than for their original purpose.

The chamfered or rounded edges of an angular object. Though it is a very slight chamfering done with a file or scraper, it makes a significant difference in feel and appearance.

A gold alloy where the silver and copper used for alloying are in equal or near-equal proportions. Generally refers to gold alloy with a golden color. Used to distinguish color tones from other colored gold alloys.

Done to reduce the weight of bulky rings or improve castability. Casting solid items with extreme thickness variations often results in shrinkage cavities or porosity, affecting the finish.

A technique of setting a stone from the inside/back of a ring. Often used when setting from the front is impossible by design, or for flat stones.

A ring profile where the inside is rounded outward (convex). If the rounding is too sharp, it feels uncomfortable, so a good sense is required. Sometimes called “yubinajimi” (finger fit).

A technique of hammering a flat metal plate into a three-dimensional shape from the back. Common methods include low-relief (usuniku) and high-relief (takaniku). Methods vary, such as using sandbags or mallets from behind, or setting in pitch and using chisels.

A casting method injecting molten metal into a mold using centrifugal force. The metal is melted, then the axis is rotated to pour it. Small personal or dental items may use manual spring-driven centrifugal machines, while factories use high-speed electric centrifugal machines.

A molding process where thick plating is the outer layer on a master mold. After thick plating, the mold is removed to hollow the inside. Allows making large, heavy-looking items lightweight. Often uses conductive, low-melting-point metals like lead, tin, or bismuth alloys for the mold. Also called “Electroforming,” which is synonymous but trademarked.

A stone showing pale to deep green. A variety of beryl with a vitreous luster. Most undergo oil impregnation. Despite high hardness, its nature makes it very brittle and difficult to handle. May birthstone. Mohs hardness: 7.5-8.

A rectangular step cut. The term is used even when gems other than emeralds are cut this way. Usually rectangular.

A general term encompassing various cloisonné techniques, including Japanese shippo, Chinese falang, and French émail. Primarily a technique of baking glassy glaze onto a metal base for decoration.

A ring given as a promise of marriage.

A thermosetting resin with epoxy groups. Used in many jewelry items because it can be ground and polished like enamel after curing. Also offers a rich color variation.

A corrosion-based process on metal surfaces. A design is drawn on the metal with a resist (ground), and it is dipped in strong acid (like nitric acid) to corrode the unpainted areas. Photo-etching transfers designs from photos.

A method of hardening where salt bath agents (sodium salts) are heated, and quenching is done in that bath.

An S-shaped link. Used for necklace or bracelet clasps. Used together with a toggle (T-bar).

A fuming, orange, mixed strong acid solution of 1 part concentrated nitric acid and 3 parts concentrated hydrochloric acid (by volume). Can dissolve precious metals like gold and platinum that regular acids cannot. However, it hardly dissolves silver because a silver chloride film forms on the surface preventing dissolution.

A copper alloy commonly called brass (shinchu). Copper alloyed with zinc, and depending on the use, tin, lead, phosphorus, beryllium, iron, aluminum, etc. Common types are 7:3 (cartridge brass) and 6:4 (Muntz metal) copper-to-zinc ratios. Since zinc has a lower melting point than copper, it vaporizes into soot during casting, causing furnace breakdowns. Recently, zinc-free copper alloys are preferred for casting.

The excess amount of molten metal added to the weight calculated from the wax model for casting. E.g., casting a ring that will be 1 gram of silver requires more than 1 gram because of the sprue system (mast, runners, etc.); the excess is the extra metal.

Another name for shibuichi. The name comes from the Edo period’s aesthetic sense of “wabi-sabi” in the tea room. It has a soft reflection, and its expression resembles the moonlight through a mist (oborozukiyo), hence the name oborogin (frosted/misty silver).

The original master model (master pattern) used when producing multiple identical design prototypes. Used for rings of the same design in different sizes or bracelet links, where rubber molding is required twice. Since shrinkage occurs twice, the master model must be made larger than the desired final product size. (A mold requiring three rubber molds is called a great master model).

An accessory threaded onto the obijime cord worn over a woman’s kimono obi. Decorates the front of the obi. Changed to enjoy different scenes according to seasons or events. Modern ones sometimes have brooch pins attached.

Originally called so because it resembled the Greek letter “Ω” when a tape material was wrapped around two chain cores. Now widely used for similar styles.

A type of cryptocrystalline quartz (chalcedony) with parallel banded patterns. Originally, only those with parallel bands were called onyx, but in modern Japan, it often refers to unbanded, solid black chalcedony, mostly artificially dyed. The only difference from agate is the shape of the bands. Mohs hardness: 6.5-7.

A general term for cuts with an elliptical outline. One of the standard cuts.

Metal that assists the flow of molten metal into the mold cavity. Mainly refers to the metal in the pouring basin. Sometimes used synonymously with extra metal. It supplies additional metal if needed and solidifies after the mold, reducing shrinkage defects.

A stone polished into a round dome shape. One of the standard cuts.

Refers to an object where a person or design is carved in relief on a gemstone or shell. Today, the main producing country for shell cameos is Italy, and for gemstone (mainly agate) cameos, Idar-Oberstein in Germany is famous.

A unit of weight for gemstones like diamonds. In ancient times in the Middle East, the carob bean was used for weighing gold (as a weight), and since one bean was relatively uniform at about 0.2g, it seems to have been used for gemstones as well. The origin of the word is the carob bean. The symbol is “ct”. 1ct = 0.2g = 200mg.

A general term for silicon carbide abrasives. Originally, the product name of the company that first manufactured this abrasive became a common noun. It is easily confused with carbon or corundum (aluminum oxide).

Refers to red to orange solid, translucent chalcedony. Mohs hardness 6.5-7. Japanese name: Beni-gyokuzui.

Cryptocrystalline quartz is called chalcedony. It is classified by color and pattern (e.g., Carnelian, Chrysoprase). Mohs hardness 6-7. Japanese name: Gyokuzui.

A method to produce luster by immersing the object to be polished in a chemical solution and promoting a chemical reaction while applying an electric current or moving the object, thereby dissolving the rough metal surface.

A gemstone that exhibits color change, showing different color tones under natural light and artificial light. Some alexandrites, garnets, tourmalines, sapphires, and spinels exhibit this color-changing property.

The forming process of cutting away a gemstone to shape it. The following items collectively describe a “cut”: 1) Shape: The overall outer shape seen from above (round, oval, baguette, etc.). 2) Style: The style of the cut (cabochon, brilliant, step, etc.). 3) Finish: The state of the polished surface. 4) Proportion: The correct geometry of the cut.

A phenomenon where a substance tries to form a homogeneous mixture when it comes into contact with another substance. It is active between gases and liquids, but less likely to occur at room temperature between solids or a solid and another state.

A method to obtain a metallurgically bonded joint by heating and applying pressure without melting the base metal, causing atoms at the joint surfaces to diffuse into each other. Also known as thermal compression bonding.

A gemstone with a glassy luster belonging to the silicate mineral group. Colors include colorless, yellow, brown, green, black, and red. The birthstone for January. Besides being a gemstone, it is used as emery for creating a matte finish, an abrasive for honing, and a grinding agent. Mohs hardness is 6.5-7.5. The Japanese name is Zakuroishi.

A traditional Japanese hair ornament used to hold bundled hair or hairstyles in place and decorate them.

A bivalve inhabiting freshwaters in Asia. It was the mother shell for freshwater pearls formerly produced in China. It was used along with the Ikecho oyster as a mother shell for Lake Biwa freshwater cultured pearls in Japan.

A system to indicate the purity of gold alloys using a 24-part scale. The symbol is K. Metal purity is usually expressed in parts per thousand, but for gold, the karat display is common. In Europe, “K” is sometimes placed at the end, like “18K”. The US uses “karat” instead of “carat” for gold. The UK uses “carat” for both gold and gemstones.

A substance used in producing nucleated cultured pearls. It is what the nacre (pearl layer) wraps around. Mostly, a shell rounded into a bead shape is inserted. In addition to shells, ceramics and artificial materials may also be used.

An industry term referring to the unit price per mass in the trading of gemstones, including diamonds. It mostly refers to “gai” = “1ct”.

The removal of oxygen atoms from an oxygen compound. Deoxidation, which extracts oxygen from metal in molten metal during casting, is a type of reduction.

The combustion flame part that has a lower temperature compared to the oxidizing flame due to an insufficient supply of oxygen.

Fixing overlapping components by passing a pin through a hole that penetrates them.

An imitation pearl manufactured using a nucleus, similar to a cultured pearl. Natural shells are often used for the nucleus, which is then coated with paint.

A substance that mixes oil and moisture to remove dirt. Soaps and detergents are also surfactants.

A casting method using water vapor pressure. A compression lid packed with asbestos containing moisture is placed over the mold into which molten metal has been poured. The moisture in the asbestos boils from the heat of the molten metal, and the vapor pressure forces the molten metal into the mold. Used for small items or single-piece production. Also known as pressure cup casting.

A phenomenon where the structural resistance of a metal increases when it is processed by applying force (rolling, forging). The distortion increases, leading to a rise in hardness and tensile strength.

An artificial crystal of zirconium oxide similar to artificial diamond. The symbol “CZ” is used.

Refers to sulfuric acid diluted with water. The concentration is typically about 10-20%, but there is no clear definition.

A technique where the base metal to be inlaid into and the cutout piece are exactly the same shape, and the cutout piece is fitted in. Also known as gankin (嵌金).

Chemical polishing mainly used for copper alloy products, immersed in a mixed “Kirinsu” solution of nitric acid, sulfuric acid, and hydrochloric acid to polish the surface or bring out the color.

Polishing that produces a mirror-like luster.

Refers to the eight metals: gold, silver, platinum, ruthenium, rhodium, palladium, osmium, and iridium.

A gemstone with high financial value. There is no clear distinction from semi-precious stones.

A transparent stone with a glassy luster and strong pleochroism (green, yellow, brown). The mineral species name that includes chrysoberyl cat’s eye and alexandrite. Mohs hardness: 8.5. Japanese name: Kinryokuseki.

Metal fittings used for necklaces and bracelets. There are various types, such as box types and fish hook types.

Glass with added lead oxide (lead glass). Those with 24% or more lead oxide are called “crystal glass,” and those with less than 24% are called “semi-crystal glass.” Used as glass for casting.

A silicate mineral. It has become common to call those with low transparency “Sekiei” and those with high transparency “Suisho” (Rock Crystal) in Japanese. For industrial use, it is called silica stone.

A phenomenon where work-hardened metal softens over time. It occurs as atoms attempt to rearrange themselves. Also called chronological softening or age softening.

Seawater non-nucleated pearls with a diameter of 2mm or more. (Those under 2mm are called seed pearls.)

Synonymous with foot press. A press machine utilizing the principle of leverage and foot power. Used for punching and bending.

The original mold that forms the basis for mass-produced cast products. Mainly created from base metal, WAX, or CAD.

Fossilized resin of coniferous trees. Typically refers to those from 30 million years ago.

Sand named for its hardness. Refers to garnet produced from Japan. Mainly used for creating a matte (pear-skin) finish.

An electric current wave with a large frequency.

A copper alloy in which 3% of “shiromi” (mica, arsenic, soap, talc) is added to copper.

A mold for mass-production casting using silicone rubber. The master model is embedded in rubber, heated and pressurized in a hot press, and then the master model is removed. Injection wax is poured into the same cavity as the master model, and that wax is then cast into metal.

A tool used to stamp metal type, carat weight, brand logos, etc., onto products. Or refers to the operation itself.

An artificially crystallized diamond with the same chemical composition and crystal structure as a natural diamond.

Placing a workpiece in acid (mainly dilute sulfuric acid) before or after soldering. A chemical treatment to remove sulfides and oxide films.

A colorless solid that hardly reacts with alkalis or acids. Used for various purposes, such as raw material for plaster used in platinum casting, and white rouge abrasive.

Applying partial plating again to the base or a plated object. Areas not to be plated are masked to avoid plating.

Raw material for green rouge abrasive.

Removing the corners of a pilot hole where a gemstone is to be set. This improves the seating of the stone when setting.

Occurs naturally as hematite. Raw material for red rouge abrasive. Also called bengara.

Small granules of bullion obtained by dropping molten silver drop by drop into water. Mainly refers to silver.

A tool used to facilitate a work process. The Japanese term ‘jigu’ is a phonetic equivalent of the English ‘jig’.

The combination of a substance with oxygen.

A film formed when metal reacts with oxygen in the air when heated to high temperatures. Removed by acid pickling.

A high-temperature combustion flame where oxygen supply is sufficient and combustion is complete.

Things hung from the waist when a man wears a kimono. Mainly includes a drawstring bag, inro (pillbox), tobacco pouch, etc.

A roughening finish created by blasting abrasive grains. Silica sand, glass powder, alumina powder, garnet powder, etc., are used as media.

A general term for all corundum other than red (ruby). Orangish-pink is called padparadscha. Usually, sapphire refers to blue sapphire. September birthstone. Mohs hardness: 9.

Refers to a matte abrasive or a matte hairline finish. Applied to a buff to create a hairline. If the buff speed is too fast, the hairline effect diminishes. Also called satin finish.

The shape of a cut gemstone seen from above. Round, marquise, pear shape, oval, octagon, hexagon, etc.

Resizing to a specified size. Mainly used for processing rings. Some cannot be resized due to shape or material.

A file finer than an oil-cut file. Also known as a light-cut file.

A file that gradually tapers towards the tip. The cross-section is rectangular. Available in sets of 8 to 12.

A phenomenon where metal (mainly alloy) increases in hardness over time. It occurs as a result of eutectic growth. There are also methods to forcibly increase hardness (such as salt bath).

A copper alloy. Zinc is added to copper, and depending on the application, tin, lead, phosphorus, beryllium, iron, aluminum, etc., are added. Zinc has a lower melting point, causing soot during casting, so zinc-free copper alloys are recently used for casting.

A mass-produced stone setting for melee diamonds, registered as a trademark in France. Now used as a term referring to the entire stone setting.

Yellow transparent quartz. November birthstone. Mohs hardness: 7.

Glassy glaze applied and baked onto a metal base such as gold, silver, or copper. Includes plique-a-jour and cloisonne. Enamel applied to an iron base is called iron enamel.

A powder made by roasting and crushing a type of diatomaceous earth yellow ocher. One of the materials mixed with pine resin, pine soot, and seed oil to make “pitch”.

A die base utilizing lead, etc. Used as a lower block for forging.

An organic substance produced by shellfish. Seawater pearls include Akoya, White-lipped, Black-lipped, Mabe, Conch, and Abalone. Freshwater pearls include Ikecho, Hireikecho, and Karasugai.

Guide holes for stone setting, which include through-holes and those that stop halfway.

Soot from burned pine wood. One of the materials used to make “pitch”.

Seawater non-nucleated pearls with a diameter of 2mm or less, though there is no precise definition. (Those over 2mm are called keshi.)

A ball formed by utilizing surface tension while melting a small amount of metal with fire.

A traditional Japanese colored metal containing 0.5 to 5% gold added to copper. When boiled (color enhanced), it becomes black to purplish-black.

Derived from the shape of the body of a Japanese shamisen. A rectangle with four outwardly rounded sides.

A traditional Japanese colored metal where the ratio of silver to copper is 1 to 3. The name and color after boiling vary depending on the ratio of silver. When blackened copper is used, it is called black shibuichi.

Plating applied as a base layer in two or more layers of plating. Examples include copper plating and nickel plating.

Casting using vacuum pressure. Also known as low-pressure casting.

An abrasive made of alumina powder hardened with oil and fat. Used for initial polishing after casting due to its high grinding effect.

A cavity defect inside a casting. It also includes porosity that occurs during soldering.

A file with longitudinal lines. Used to apply a lined texture to workpieces.

A varietal name referring to colorless and transparent quartz. Mohs hardness: 7.

A small crucible for melting small amounts of platinum.

Generally yellow or green, but highly pleochroic, and rarely red is also produced. One of the birthstones for July. Mohs hardness: 5.5.

A gemstone that occurs in a wide range of colors including blue, green, red, pink, purple, orange, black, and colorless. Mohs hardness: 8.

A ruler for determining a 90-degree angle.

A phenomenon where a gemstone emits a star-like ray of light under a point light source. Asterism is synonymous with the star effect.

A cut with square facet planes arranged in a stair-like manner. One of the basic cuts.

A silver alloy containing 92.5% silver. The remaining 7.5% is mainly copper to improve workability and durability. Products stamped with “925” are sterling silver.

The part connecting a clasp and a chain that rotates to eliminate twisting, or the entire fitting.

A metal with a silver-white metallic luster. Tin plating on an iron plate is known as tinplate. Also used inside copper cookware. High purity tinware is used as daily necessities under the name pewter.

A copper alloy mainly consisting of 90% copper and 10% tin. Used for sculptures and Buddhist statues.

A casting method for creating castings where detail and dimensional accuracy are important. Includes investment casting (lost wax), Shaw process, and Unicast method.

Refers to opaque or translucent quartz. Transparent quartz is called rock crystal.

A pattern with continuous semi-circular arch shapes representing waves.

The technique of embedding a different metal into a base metal. Also applied to wood, gemstones, and ceramics. Embedding metal into organic materials like tortoiseshell or ivory is called piqué.

The classification of gemstones by size, color, quality, etc.

A commercial concept proposed by the American jewelry industry in 1912 associating specific gems with months of the year.

An iron alloy with a carbon content ranging from 0.02% to 2%.

A flat tag attached to chains, used as a counterpart for spring rings and lobster clasps. Originally made from round wire resembling a Daruma doll, hence its Japanese name. Now mostly press-punched.

A common name for copper sulfate. Used in traditional metal coloring.

A stick-like tool mainly made of carbon steel. By striking the top with a hammer, it is used for repoussé, engraving, cutting, and texturing. A crucial tool in metalwork.

A type of accessory worn by men mainly in the Edo period. Often attached to the obi with a netsuke. Metalwork techniques are used for the front clasps of the pouches.

Removing oils and fats attached to the metal surface before plating, coloring, or soldering using a degreasing agent (organic solvent, alkaline, or acidic degreaser).

The removal of oxygen dissolved in molten metal by reduction. Deoxidation is a type of reduction.

Heating the mold to allow the wax inside to flow out.

A natural cubic crystallized carbon mineral. Exists in colorless, brown, yellow, and fancy colors. Birthstone for April. Mohs hardness 10.

A method of applying continuous cuts to the surface of products made of gold, platinum, etc., by rotating a diamond bite. Changing the bite shape, speed, and direction creates various patterns. The cut surfaces are highly reflective.

A casting method in which molten metal is poured into a precisely crafted metal mold under high pressure and at high speed. Used for machine parts, automobile parts, etc.

A stone made by pasting two different materials together (top and bottom) and polishing them.

A technique utilizing the excellent ductility of metal. A metal plate is hammered and shaped into vessels using a metal or wooden hammer against an anvil.

A forging technique using tools and molds to compress or strike metal into shape. It also makes the metal structure finer and more uniform.

Pearls produced by bivalves inhabiting freshwater areas such as rivers, lakes, and marshes in Japan, China, America, and Europe. Most on the market are cultured pearls.

A three-dimensional repoussé technique that uses thick metal plates to create deep, pronounced relief forms.

A copper alloy of copper and zinc. Contains less zinc compared to standard brass.

A file with teeth cut in only one direction. Suitable for working with soft metals, resins, and wax.

Striking a product with a stamp indicating its material, purity, carat weight, or trademark.

A translucent to opaque stone with a pearly or greasy luster. The main ingredient in talcum powder. Mohs hardness 1.

A mixture of talc and boric acid. Used as a release agent for wax.

A copper alloy with equal parts copper and brass. Turns orange to earthy red when boiled for color.

The commercial name for blue to bluish-purple zoisite, named by Tiffany & Co. after its place of origin, Tanzania. A December birthstone. Mohs hardness 7.

A narrow accessory designed to clip onto a tie. Various clasps such as alligator clips or push pins are used.

An accessory with a pin on the back, inserted through a tie and secured with a catch on the reverse side.

Tack-style brooches, lapel pins, school badges, company badges, etc.

An opaque resin-luster stone in blue, blue-green, etc. The blue color comes from copper, and green from iron. Birthstone for December. Mohs hardness 6.

The process of drawing out gases from the slurry invested in a casting flask using vibration and vacuum suction.

A flush setting where the stone is embedded at the bottom of a cup-shaped seat larger than the stone. Named for its resemblance to an ochoko (sake cup).

A classical term referring to metal casting.

The technique of creating objects by pouring molten metal into a mold. Most modern jewelry is produced using this method.

A steel alloy of tungsten-cobalt or tungsten-titanium-cobalt carbides. Excellent wear resistance and used for cutting tools.

Components linked or woven continuously. Designs are endless depending on material, thickness, size, and shape.

A cut style where square facets form a grid pattern on the table surface, making it look like a checkerboard.

A chisel that creates a pattern resembling bird footprints. A type of texturing chisel.

Processing techniques using chisels to engrave patterns or letters on metal plates or cast items. Includes hairline engraving, inlay, and granulation.

Coral harvested along the Mediterranean coast. Similar to Japanese red coral but characterized by the absence of white spots (fu).

Dark red coral highly prized for jewelry. Found off the coast of Kochi Prefecture in Japan. Large pieces are extremely rare.

Making uneven surfaces completely level with one another.

A surface finish applied by striking the object with a hammer or a hammering chisel to leave hammer marks.

An abrasive made from burnt and powdered deer antlers. Used for polishing lacquer, tortoiseshell, ivory, etc.

A finish that removes the gloss from a metal surface.

A finish or processing stage that brings out the gloss of a metal surface.

The sword guard fitting placed between the blade and the handle of a Japanese sword.

Refers to the weight of the precious metal bullion used in a product.

An abbreviation for deluxe frame. A luxurious and highly processed setting, such as those with surrounding stones or tapered accents.

A heating furnace using electricity as a heat source. Used for wax removal and baking molds in jewelry making.

A phenomenon where applying DC voltage to electrodes in an ion-conductive solution causes chemical reactions at the electrode interfaces.

Metal polishing utilizing electrolysis. The object acts as the anode in a solution, dissolving to produce gloss. Effective for complex areas where buffs cannot reach.

A surface treatment where the object is submerged as the cathode in a solution of ionized metal, and DC current causes the metal to deposit onto the object.

A forging process where a cylindrical material is pressed against a die and rotated to form screws or rivets.

A general term for alloys with a melting point lower than that of tin (230°C). Often composed of tin, bismuth, and lead. Used for rubber casting.

The physical property of metals that allows them to be hammered flat (malleability) or drawn into wire (ductility) without breaking.

A process of polishing the top part of the stone seat at an angle to reflect light and make the center stone shine more beautifully.

A basic cut where one end of a baguette cut is polished thinner, creating a taper.

A bracelet made of a continuous line of individually set diamonds. Named after Chris Evert dropped hers during a 1987 US Open match.

Effects applied to the surface of a product. A finish that enhances value by altering color, texture, and gloss using chemicals, abrasives, and tools.

A type of anvil with a pointed tip resembling a bird’s beak.

Powder from scraped whetstones or roasted yellow clay. Used for polishing swords.

Using the same material as the workpiece as an abrasive, or grinding two joined different materials together.

Melting and joining base metals together without using soldering material. Accurately called welding.

Similar to a bezel setting, but the stone is set flush with the surrounding metal.

A design where the center stone is surrounded by smaller stones. Can be double-layered as well.

A transparent glassy stone in colors like blue, yellow, and brown. F Type (fluorine) is produced outside Brazil. Most blue topaz is irradiated. November birthstone. Mohs hardness 8.

A transparent glassy stone in golden, orange, pink, or red. OH Type (hydroxyl) is from Minas Gerais, Brazil, and is also called Imperial Topaz. November birthstone. Mohs hardness 8.

Soldering using a gas flame as the heat source.

Refers to a small handheld burner used for soldering.

A silicate mineral occurring in various colors. When heated, it becomes electrically charged. Pink is rubellite, blue is indicolite, and copper-bearing is Paraiba tourmaline. October birthstone. Mohs hardness 7.5.

A stone used to sharpen tools or polish stones. Natural whetstones include sandstone, while artificial ones use emery or diamond grains.

Softening a hardened metal by heating and then cooling it, though it varies by metal type. Heating and cooling adjust the crystal structure and remove internal stress. Also called solution treatment.

A continuous pattern created by striking a workpiece with a small concave chisel called a nanako tagane, forming a fish-roe-like texture.

The main gemstone placed in the center or the most emphasized position of jewelry.

A surface finish that involves dropping emery (garnet) grains onto a workpiece to create a matte texture.

Components other than the gemstone found inside a gemstone. Gas, liquid, or solid trapped within the crystal as it grew. It can show unique characteristics of the gem.

A grayish, bluish metal. Soft and heavy. Excellent malleability allows it to be processed into thin sheets, but poor ductility makes it unsuitable for fine wire. Used for water pipes, X-ray room linings, and solder. Used as a die base in metal engraving.

Glass containing 24% or more lead oxide. Used for crafts and tableware. Since it can be poured into plaster molds, it can create complex shapes.

Refers to marine white-lipped and black-lipped pearl oyster pearls, as opposed to Akoya pearls. Also known as Nanyo pearls.

An adhesive made from collagen extracted from animal hides and bone marrow.

Traditional Japanese colored metals like shakudo and shibuichi develop their color by being boiled in a mixed solution of copper sulfate, verdigris, and water. This coloring method is called Niiro finish. The metal is cleaned of oxidation and oils, and often soaked in grated daikon radish before boiling. This method has not changed since ancient times.

A two-tiered setting for a gemstone. Used to adjust the height from the pavilion to the culet of the gem.

An industry term for white gold alloy using nickel. Due to nickel allergy issues, its use is often avoided nowadays.

A technique where grooves for patterns are carved into gold or silver, and a black alloy of lead sulfide, silver, copper, and gold is melted into the grooves to create a striking contrast.

A polishing tool made of circular cutouts of layered cloth. Attached to a buffing motor or a hand router and used with an abrasive.

An inlay technique where fabric-like grooves are carved into a hard metal plate like iron using a specific chisel, and thin pure gold or silver is pressed into it to create patterns.

A press machine where the slide is operated by manual hand power. Synonymous with Neko Press.

Operations such as quenching, tempering, and annealing of metal, or changing its properties through these operations.

Imitation gemstones made using natural stone powder, resin, glass, or bone by press molding. Examples include imitation coral and bone turquoise.

An ornament worn around the neck. Names vary depending on the length and shape.

A miniature sculptural accessory attached by a cord to small suspended items like an inro, tobacco pouch, or coin purse. Made from various materials like ivory or boxwood.

The phenomenon of heat transferring through an object from a high-temperature area to a low-temperature area.

The increase in volume of an object as its temperature rises under constant pressure.

A large hammer with a flat face and a pointed reverse end. Used for flattening and extending metal plates or square rods.

Knots tied between beads on expensive pearl necklaces. Prevents pearls from scattering if the thread breaks and prevents them from rubbing against each other.

A rectangular cut. One of the standard cuts. “Baguette” means stick or rod in French.

A bracelet in the shape of a rigid ring.

A highly misshapen pearl. A natural shape.

Grinding and polishing by friction, achieved by placing workpieces, abrasives (media), and polishing compounds in a rotating or vibrating container. Barrel tanks are common. Used for mass grinding and polishing.

A state where two colors are distributed with a clear boundary within a single crystal. E.g., agate, tourmaline, sapphire.

Polishing using a buff attached to a buffer or hand motor.

A cut shape where the upper part above the girdle is polished in a curved surface like a cabochon, and the lower part is processed into various faceted cuts.

A file whose cross-section is half-round on one side and triangular on the back.

An extremely high-quality cultured pearl that has not undergone color tone processing.

Molded high-melting-point paraffin wax. It can be cut, carved, and filed. Using a wax pen, wax can also be added.

An accessory pinned into the hair to keep a hat from falling off the head.

A pattern seen in a brilliant-cut diamond, showing a heart mark from the pavilion side and an arrow mark from the table side. Heart & Arrow is a registered trademark.

Synonymous with Heart & Arrow. Since Heart & Arrow is a registered trademark, Heart & Cupid (H&C) is generally used.

Also known as high-speed steel. A tool steel made by adding large amounts of alloying elements like chromium, molybdenum, tungsten, cobalt, and vanadium to high-carbon steel. Used for molds and cutting tools. Suitable for high-speed cutting and resists frictional heat. Divided into tungsten and molybdenum types.

A polished gemstone that has not been set into a mounting, intended for sale or processing.

Sapphires that have only an intermediate color between orange and pink. The only sapphire with an independent name other than ruby. Means lotus flower in Sanskrit.

A type of platinum group metal. Used as an alloying material for platinum.

An industry term for platinum or white gold alloyed with palladium.

A state where three or more colors are distributed within a single crystal. E.g., watermelon tourmaline.

A technique of molding by placing powdered lead glass into a plaster mold and heating it.

The part below the girdle in a faceted cut.

The part at the top of a pendant fitting through which the chain passes. Named because its shape resembles a shamisen plectrum (bachi).

Refers to six elements: ruthenium, rhodium, palladium, osmium, iridium, and platinum.

A soldering material with a lower melting point due to a high ratio of brass or zinc to silver. Used for temporary tacking.

Often refers to gemstones other than diamonds, rubies, sapphires, emeralds, and rare stones, although there is no clear distinction.

The ability to return to its original shape after being deformed by a certain force.

The proportion of the primary metal contained in a precious metal alloy. Mostly expressed in parts per thousand, but carat notation remains customary for gold.

A hearth made of firebricks used for melting operations.

Stains from copper content or mixed films of oxidation and sulfuration appearing on the surface of silver alloys after heating. Difficult to remove by buffing alone.

An inlay where the base metal and the inlaid metal are completely flush with each other.

A white to green stone with a vitreous luster. Jadeite (hard jade) is referred to as jade, but nephrite (soft jade) is sometimes included. They are entirely different minerals but hard to distinguish by appearance. Mohs hardness 7.

Parts produced by lathe machining.

A ring worn on the little finger.

Refers to diamonds with very low clarity and extremely low commercial evaluation.

The technique of inlaying metal parts such as gold or silver into organic materials like tortoiseshell, ivory, coral, shell, and pearl. Popular during the mid-Victorian era.

The shell that produces conch pearls.

Shrinkage after casting. The occurrence of depressions in thick sections or near the center of flat surfaces.

A clasp consisting of a round pipe containing a spring connected to a core rod, allowing it to open and close. Most commonly used as a necklace clasp.

A device to forcefully send air into a fire grate. A small bellows operated by foot is called a tanuki.

A stone setting where the metal rim (flange) around the stone is evenly pushed inward against the stone. Also called flush setting.

Chalcedony with red spots on a dark green base. A March birthstone.

A general term for ornaments worn around the wrist.

A cut with many facet planes. The most representative facet cut for gemstones.

An ornament pinned to clothing.

A unique industry unit primarily expressing the mass of a diamond under 1 carat. If 1 carat is 10 bu, a 0.3ct stone is a 3-bu stone. 1 bu equals 10 rin.

The numerous flat polished surfaces in a gemstone cut.

A cut composed of many flat surfaces. Mainly used for transparent stones.

Among faceted cuts, those that do not fall under brilliant, step, emerald, or mixed cuts, or cuts other than brilliant. Or those composed of facets other than triangles, rhombuses, and rectangles.

A gas similar to chlorine, one of the halogen elements. Hydrogen fluoride not only has ordinary acidic properties but also special properties that dissolve glass and silicon-containing investment materials for casting.

A soldering additive in powder, paste, or liquid form. It promotes the wettability and flow of the solder. It also prevents metal oxidation. Components include boric acid, borates, fluorides, borofluorides, carbonates, and chlorides. Highly corrosive, so it is removed with dilute sulfuric acid after soldering.

An imitation pearl manufactured using a plastic nucleus.

A representative of the platinum group metals. Belongs to heavy platinum. Boiling point (3827°C), melting point (1769°C).

An alloy for jewelry mainly consisting of platinum. Expressed in parts per thousand like 950, 900, 850, depending on the proportion of alloying materials.

A machine or process used to form, cut, punch, draw, bend, coin, or forge materials by applying pressure from above and below using a mold.

A square facet cut that does not have a table on top.

In the industry, the smelting and refining of buffing powder and dust collector debris is called refining (analysis).

A technique of melting different base metals separately and casting them alternately into a single mold.

The ratio of the finished product weight to the raw material weight.

Called goshenite when colorless, aquamarine when seawater blue, morganite when pink, heliodor when yellow-green, bixbite when yellow, golden, or red, pezzottaite when deep pink, and emerald when green. When simply called beryl, it refers to a pale yellow color. Mohs hardness 7.5-8.

A copper alloy containing 0.4 to 2.2% beryllium and trace amounts of cobalt, silicon, and iron.

A phenomenon where the color of a gemstone changes under natural light versus incandescent light. Alexandrite is a representative example.

The amount of bullion consumed and unrecoverable during the manufacturing process. Or the estimated bullion loss expected during processing.

A general term for cuts shaped like a pear or a teardrop.

A hanging ornament worn on a chain around the neck. Pendant top is synonymous.

A transparent stone with a vitreous luster in yellow or yellow-green. An August birthstone. Mohs hardness 6.5-7.

A translucent resin-luster material utilizing the shell of the hawksbill sea turtle.

Colorless, odorless, scaly crystals with a pearly luster. Soluble in warm water. Has better coating properties than borax, so it is mixed with borax and used as a flux. Formula: H3BO3.

Glass made mainly of silicon oxide with boric acid, soda or potassium oxide, and aluminum oxide. Used for Pyrex glass, laboratory glassware, and heat-resistant items.

Opal that crystallizes thinly inside the country rock.

In a broad sense, the rock belt that nurtures and surrounds a mineral deposit. Opals and others are often formed containing parts of the ore.

A machine that drills holes in a workpiece through the rotational and vertical movement of a spindle fitted with a drill.

A machining method that creates a mold by causing an electrical discharge phenomenon between the workpiece and an electrode, transferring the shape of the master electrode to the workpiece using a machine tool that mimics shapes or cuts. Used in the manufacture of stamping dies.

Baking a glaze onto a metal surface, firmly coating it with a glass membrane. Basically the same as cloisonné, but since the Meiji era, the term enamel (horou) has been used when iron is utilized as the base metal.

The operation of carving into metal using a chisel and hammer. A technique to create indentations, letters, patterns, and surface effects on a workpiece.

Setting a gemstone using prongs raised by carving the workpiece with a chisel.

Refers to a precious metal purity certification by a public institution, such as the Mint’s purity certification mark.

In the jewelry industry, it refers to obtaining a texture by blasting sand particles onto the surface of a workpiece.

A machine or process that creates a rubber mold by applying pressure and heat to unvulcanized rubber.

Charcoal made from magnolia wood. Used for charcoal grinding. Often hollowed out and used when making granulation balls.

Wood from the Magnoliaceae family used for bench pins and wood buffs. It has little grain and a moderate hardness. Said to have the property of not rusting bladed tools.

Shells inhabiting seawater or freshwater used for pearl cultivation. Seawater ones include Akoya, Black-lipped, and White-lipped oysters, while freshwater ones include Ikecho and Hireikecho mussels.

A 1/100ct melee stone.

An alloy made by adding white alloying materials like palladium to gold. Depending on the type and ratio of the alloy, it is not perfectly white, so products are often rhodium-plated.

Pouring liquid plaster (investment material / slurry) into a flask (casting ring) containing a wax tree.

Refers to the mother oyster used to produce half-round cultured pearls, or its loose pearl.

Chains manufactured by automatically weaving standardized designs in large quantities using automated machines.

A boat-shaped facet cut with pointed ends. Synonymous with navette cut. One of the basic cuts.

A ring indicating marriage. Synonymous with wedding ring or wedding band.

A set of diamonds with standardized colors used to determine the color grade of other diamonds.

An engraving setting where the area around the stone is cut into a square shape.

A general term for pearl mother oysters. Includes Akoya, White-lipped, and Black-lipped oysters. Processed and used as a gemstone.

A natural resin secreted from pine trees. One of the raw materials for pitch used to fix workpieces. Also a raw material for beeswax.

Wax made by mixing beeswax, pine resin, paraffin wax, etc.

Setting a stone using small, continuous bead-like prongs created with a milgrain tool.

Decorating with small continuous beads using a milgrain tool.

Beautiful feldspar classified as a gemstone. June birthstone. Mohs hardness 6.

A pearl without an artificial solid nucleus. Natural seawater pearls, cultured Keshi pearls, and most freshwater pearls are non-nucleated. Not necessarily natural; non-nucleated cultured pearls are cultured by inserting only mantle tissue into the mother oyster.

A type of banded chalcedony. Agate is a subcategory of chalcedony. Chalcedony with layered bands is agate.

Refers to small diamonds of 0.1ct or less.

Decorative metal fittings attached to the hilt (tsuka) of a Japanese sword.

Coating the surface of a product with a thin film of another metal. Used not only for aesthetics but also for corrosion resistance, wear resistance, and surface hardness.

A standard for measuring minerals and gemstones devised by German mineralogist Friedrich Mohs in 1822. It ranks hardness on a scale of 1 to 10. It is a relative hardness, not an absolute one.

A metalworking technique where different metals are diffusion-bonded (without solder), carved, and rolled out thinly to create a wood-grain pattern.

Softening a hardened metal by heating it and then allowing it to cool. Also called solution treatment.

A punch with a spherical tip. Used together with a dapping block for forming domes or half-spheres.

A hand tool used to shape workpieces by filing the surface. Selected based on size, shape, tooth pattern, and fineness.

A scissor-like tool with two jaws and handles. The jaws are modified to suit the workpiece. Used for gripping, pulling, bending, twisting, etc.

An operation to increase the strength of metal by rapidly cooling it after heating. Mainly used for tools like chisels and blades made of steel.

Reheating quenched metal below its transformation point to reduce hardness. Quenched steel chisels are too hard and brittle, so they are tempered to give them flexibility.

An industry term for pure gold. Derived from the Edo period practice of mixing rough gold with salt and burning it to remove silver (salt and silver combine to form silver chloride, separating the pure gold).

A compound of melted pine resin, pine soot, clay powder, and seed oil. Used to hold workpieces securely during repoussé, engraving, stone setting, or gem polishing.

The inner part of a ring that touches the finger. Without a good finger fit, a ring with sharp inner edges feels very uncomfortable.

The entrance where molten metal flows into the mold. The position and shape of the sprue affect casting precision.

Metal in a melted, fluid state, primarily during casting.

Pearls cultured by inserting a shell nucleus and mantle tissue into the mother oyster. Most seawater cultured pearls (Akoya, South Sea) are nucleated.

The four standard elements indicating a diamond’s grade: 1. Carat (weight), 2. Cut, 3. Color, 4. Clarity.

A copper alloy with added zinc and nickel (8-20%). The color is silvery-white. Also known as German silver or Alpaca. Originally developed in the UK but named German silver because it was widely used in Germany.

A purplish to deep blue opaque stone composed primarily of lazurite, along with sodalite, hauynite, and noselite. Those with golden flecks contain pyrite. September and December birthstone. Mohs hardness 6.

Jewelry with decorative elements at both ends, worn by wrapping or tying rather than connecting with clasps.

A deep blue to green opaque stone with a vitreous luster. The main component of lapis lazuli. Mohs hardness 5.

A general term for all facet cuts with a circular outline. The most common and widely produced shape. One of the basic cuts.

A casting method using centrifugal force to pour low-melting-point (under 400°C) metals into spinning, heat-resistant silicone rubber molds. Suitable for mass-producing inexpensive items using tin alloys, antimony, white metal, etc.

An ionic compound of copper(II) ions and sulfate ions. Used with verdigris for coloring traditional Japanese alloys (shakudo, shibuichi).

A technique of fusing a large amount of tiny gold granules onto a surface. Artifacts from ancient Etruria are famous for this.

Remaking owned jewelry. Utilizing gemstones, frames, or parts to create new jewelry. Synonymous with remake or redesign.

A copper alloy containing tin (3.5-9%) and phosphorus (0.3-0.35%). Excellent wear resistance, corrosion resistance, and elasticity, so it is often used for spring materials.

Bullion refined and analyzed from scrap metal brought to precious metal dealers, trade-ins during remodeling, or manufacturing scraps. It holds the same value and properties as newly mined metal.

A compound formed when sulfur reacts with silver. Sometimes intentionally applied to create oxidized silver products. Formula: Ag2S.

A corrosion phenomenon caused by the reaction of metal with sulfur or sulfur compounds (hydrogen sulfide). The tarnishing of silver is mainly due to sulfidation, which is different from oxidation (rusting).

A colorless, odorless, viscous liquid inorganic acid. Mixes with water and generates heat. Highly acidic, dissolving most metals except gold and platinum.

A container used for high-temperature processing like melting metals. Made from refractory materials like porcelain, graphite, or alumina.

A cut and processed gemstone before it is set into jewelry. Synonymous with naked stone (raseki).

Red corundum colored by chromium oxide. Transparent with a vitreous luster. Mohs hardness 9.

A platinum group metal. Used for alloying or plating. Boiling point 4155°C, Melting point 2250°C.

Quartz containing needle-like inclusions of rutile visible to the naked eye. Mohs hardness 7.

A black, brown, red, purple, blue, or green stone with a metallic luster. Known for causing the star effect in rubies/sapphires or as inclusions in quartz. Mohs hardness 6.

A setting method where stones are lined up and secured between two metal tracks like rails.

A method of engraving text, symbols, or designs using a laser marker fed with AI data, rather than striking the object directly.

A method of welding metals together using the localized heat of an irradiated laser. Since thermal conduction is low, it can be done while holding the piece by hand.

Joining metals using a filler metal (solder) on the heated base metal. Joining with filler melting above 450°C is hard soldering (brazing), while below 450°C is soft soldering.

The visible trace or seam left after soldering.

The most widely used technique in jewelry manufacturing. A wax model is invested in plaster, the wax is melted out (dewaxed), and molten metal is poured into the resulting cavity. Includes centrifugal, vacuum, and pressure casting.

A unit of trade referring to a grouped quantity of processed gemstones.

A platinum group metal. Excellent in reflectivity and hardness, making it widely used for plating. Boiling point 1960°C, melting point 3697°C.

The blue-green to green rust that forms on the surface of copper and copper alloys. It is not toxic.

Metals added to a primary metal to establish its purity, color, melting point, or workability.

The metal framework created to hold a gemstone, referring to the entire piece excluding the gem. Includes cast, pressed, and handmade mountings.

Smaller stones arranged next to the center stone.

When stones are set in a line, a single prong between two stones is split to hold both adjacent stones. A shared prong, in contrast, uses one undivided prong to hold two stones.

Viscous organic substances with an alkyl group and a melting point below 110°C. Can be mineral, plant, or animal-based. Soluble in oils, alcohol, and ether, but not water. Includes beeswax, paraffin, hard wax, and injection wax.

A master model carved primarily from hard wax (green, purple, or blue high-melting-point paraffin wax). Can be hand-carved or milled using CAD data on a CNC machine.