Paste
The Encyclopedia of Founding (1892)
Important: Safety Warning
This page contains a formula or preparation using substances now known to be dangerously toxic, such as arsenic, mercury, lead, or cyanide compounds. Exposure to these substances can cause severe poisoning, permanent injury, or death.
In addition, this page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
Foundry-paste is simply flour mixed with water to a consistency suitable for the joining together of dry-sand cores and moulds that are made in sections. It may also be used in the coring of moulds when it is desirable to effectually prevent the escape of metal at the points of junction, its spreading quality permitting the soft, yielding mass to be forced into every crevice, where, if the mould be hot enough, it dries into a hard impenetrable mass. There is much danger, however, in using too much paste, especially in cold moulds. When the molten metal enters the mould the wet surfaces are at once converted into steam, which, if not all ejected during the process of casting, seldom fails in producing blow-holes at some part or other. See SIZE; BLISTER; BLOW-HOLES. Paste Gems are a glass imitation of precious stones, made from a combination of silica, potash, borax, red oxide of lead, with some arsenic. This is fused gently in Hessian crucibles, in the furnace, for about twenty-four hours, and it then becomes a base for the manufacture of all the spurious gems. For the ruby, 72 parts of oxide of manganese are mixed with 2880 parts of the paste; emerald--green oxide of copper 42, and oxide of chrome 2, to paste 4608 parts--sapphire: oxide of cobalt 68, to paste 4608 parts; fused for thirty hours. Amethyst--oxide of manganese 36, oxide of cobalt 24, purple of cassius 1, to paste 4608. The tints of the real stone are so exactly imitated in many of these imitations as to deceive any but the best judges. See PRECIOUS STONES.
What Has Changed in the Last Century
The 1892 warning about moisture and blow-holes still holds, but flour-and-water joint paste has largely gone: since the 1950s the sodium-silicate/CO2 process and chemically bonded resin sands have let cores be assembled with commercial refractory core pastes and sealants that add little water to the mould. The bigger change is in the second half of the entry. Verneuil's flame-fusion process, commercialised from about 1902, made it possible to grow genuine synthetic ruby and sapphire — real corundum, not lead glass — and cubic zirconia, developed in the 1970s, took over as the standard diamond simulant. Lead-glass "paste" survives mainly as costume rhinestone, and the arsenic the recipe calls for has been driven out of glassmaking by modern occupational-health rules.
Written for this edition, 2026.