Book - Appendix A - Definitions

Appendix A - Definitions

Knowing the meanings of words is important to anything you do.  Mold making and casting has a number of unique words to the craft and here we try to clear some of the fog that may arise by supplying a few definitions.

Accelerator

A substance which increases the rate of cure.

Alginate

Any of several derivatives of alginic acid derived from seaweed or sodium alginate reacted with calcium salts for making masks and castings.

Alloy

To mix, as metals, so as to form a compound.

Block Mold

A term used in mold making to describe a mold in which the silicone completely fills the area between the master and mold support. The exterior of the mold does not conform to the shape of the master.

Casting

To form (liquid metal, for example) into a particular shape by pouring into a mold.

Catalyst

A substance used to significantly accelerate a chemical reaction.

Concrete

A hard, strong construction material consisting of sand,conglomerate gravel, pebbles, broken stone, or slag in a mortar or cement matrix.

Cure Time

The time a sealant takes to develop its full properties.

Curing

To prepare, preserve, or finish (a substance) by a chemical or physical process. To vulcanize (rubber).

Degassing

To remove gas or air from.

Die Stone

A dental product made from gypsum that has a compression strength usually over 18,000 PSI.

Form

A mold for the setting of concrete, plaster, silicone or other agent until it cures.

Gypsum

A widespread colorless, white, or yellowish mineral, CaSO4·2H2O, used in the manufacture of plaster of Paris, various plaster products, and fertilizers.

Latex

An emulsion of rubber or plastic globules in water, used in paints, adhesives, and various synthetic rubber products.

Ladle

A vessel to carry liquid metal from the smelting pot to the mold.

Lead

A soft, malleable, ductile, bluish-white, dense metallic element, extracted chiefly from galena and used in containers and pipes for corrosives, solder and type metal, bullets, radiation shielding, paints, and antiknock compounds. Atomic number 82; atomic weight 207.2; melting point 327.5°C; boiling point 1,744°C; specific gravity 11.35; valence 2, 4.

Library Life

A term referring to the length of time a mold can sit in storage with deteriorating.

Master

Being an original from which copies are made.

Mold

A hollow form or matrix for shaping a fluid or plastic substance.

Mold lines

Lines showing up on the finished cast caused from molds made up of two or more pieces.

Naphtha

Any of several highly volatile, flammable liquid mixtures of hydrocarbons distilled from petroleum, coal tar, and natural gas and used as fuel, as solvents, and in making various chemicals.

Negative

The reverse impression of the master that is left in the mold.

Pewter

Any of numerous silver-gray alloys of tin with various amounts of antimony, copper, and sometimes lead, used widely for fine kitchen utensils and tableware.

Plaster

A mixture of lime or gypsum, sand, and water, sometimes with fiber added, that hardens to a smooth solid and is used for coating walls and ceilings or casting figurines and other items.

Potlife

The term referring to the cure rate of a silicone RTV.

Pressure Casting

A casting technique of using compressed air in a pressure pot to reduce or help eliminate air bubble from castings. Typically used when casting resins.

Pressure Pot

A specially designed container for casting under pressure.

Pulls

An expression referring to the number of parts obtained from a mold.

Release Agent

A compound or solution to allow a newly cast object to be released from it's mold. Or to keep the original from sticking to the mold making material.

RTV

RTV Silicone are a rubber like polymer called polydimethsiloxanes. RTV stands for room temperature vulcanizing, or simply a rubber which cures at room temperature. Silicone rubber adhesives are made from a complicated process that turns elemental silicon metal made from sand (silica) into a rubbery polymer. When cured, silicone rubber adhesives/sealants have excellent resistance to heat (500-600ºF) and moisture which makes them exceptionally suited for outdoor weathering applications, such as sealant and caulking compounds in the construction industry. A silicone rubber usually of a two part composition which cures at room temperature. RTV silicone moulds typically yield upwards of 100 or more casts with incredible detailed reproduction of the pattern.

Shelf Life

The amount of time a product may be used without deterioration.

Shore Hardness

A scale of measurement used to describe the hardness of a material when measured with a durometer. There are three commonly used scales, in degrees of increasing hardness: Shore 00, Shore A and Shore D.

Slip Mold

A mold usually made of latex that when filled with casting media is pulled off the casting like a slip.

Smelt

To melt or fuse (ores) in order to separate the metallic constituents.

Split Mold

A two piece mold used to create castings that could otherwise not be made with a single mode or slip mold.

Tear Strength

A test technique used to measure the force required to initiate or propagate a tear into a material sample, measured in pounds per inch "PPI".

Tensile Strength

A method to measure the force required to rupture the material (stress-strain at break) per unit area subjected to a specific dynamic load, usually expressed in pounds per inch.

Tin

A malleable, silvery metallic element obtained chiefly from cassiterite. It is used to coat other metals to prevent corrosion and is a part of numerous alloys, such as soft solder, pewter, type metal, and bronze. Atomic number 50; atomic weight 118.71; melting point 231.89°C; boiling point 2,270°C; specific gravity 7.31; valence 2, 4.

Undercuts

A term describing the complexity of a shape; these areas are very deeply indented or cut, and therefore require that the mold be pulled and stretched around them in order to remove the mold.

Vacuum

A space in which the pressure is significantly lower than atmospheric pressure.

Vacuum Chamber

A Specially designed chamber that is designed to hold a vacuum.

Vacuum Pump

A mechanical device designed to remove air from a vacuum chamber.

Vaseline

A yellowish translucent substance, almost odorless and tasteless, obtained as a residue in the purification of crude petroleum, and consisting essentially of a mixture of several of the higher members of the paraffin series. It is used as an unguent, and for various purposes in the arts.

Vent Channels

Channels cut into a mold to allow the escape of air.

Viscosity

resistance of a liquid to sheer forces (and hence to flow)

Wet Water

Water that has had a small amount of liquid soap mixed in with it to reduce the surface tension of the water.

Worklife

A term used to indicate the amount of time an end user has to work with a curing silicone.