Mending-up
The Encyclopedia of Founding (1892)
Important: Safety Warning
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.
The art of repairing broken surfaces in the mould which may have been caused by accident, carelessness, or faulty models or patterns. This phase of the moulder's art calls for the nicest manipulation, with delicate fashioning-tools made for the purpose. See FINISHING. Mercury or Quicksilver.--A metal always fluid in our climate, but solidified by intense cold into a malleable metal resembling silver. It is found native as well as combined with sulphur, when it is called cinnabar. But cinnabar is easily reduced at a red heat to the metallic state by the action of iron or lime, or atmospheric oxygen; the sulphur being extracted, when iron is used, as sulphide of iron; when lime is used, as sulphide and sulphate of calcium; and as sulphurous-acid gas when oxygen is used. The alchemists of old did not believe mercury to be a true metal, because they were unaware of its susceptibility to freezing into a compact solid. With the exception of iron and platinum, mercury will readily unite with all metals into an amalgam. (See AMALGAM; AMALGAMATION.) Liquid amalgams of the precious metals are largely used for gilding and silvering objects which have been made in baser metals. The amalgam is spread over the object with brushes, after which the mercury is driven off by the application of heat, leaving a film of the nobler metal firmly adhering to the object treated. Mercury has a great affinity for all other metals that are soluble in mercury; for if an object be dipped into it there is great difficulty in rubbing off the mercury, which immediately adheres to it. If mercury is rubbed over tin-foil, it unites in one mass and forms an amalgam, as is the case with mercury and lead. When lead and bismuth are mixed with mercury, the amalgam will be equally fluid with the mercury itself. This important metal is used for barometers, thermometers, silvering looking-glasses, and for many other useful purposes, including the making of vermilion. It is largely employed in separating the precious metals from extraneous matter. Mercury is the heaviest of all metals except gold and platinum; consequently silver, iron, lead, etc., float upon it as wood does upon water. The production of mercury (1882) in Austria was 542 tons; Italy, 55 tons; Spain, 929 tons; United States (principally Almaden, Cal.), 2054 tons. See TIN; AMALGAM; FLUID ALLOY; METALS.
What Has Changed in the Last Century
The mending of damaged sand moulds by hand, which the Encyclopedia of Founding called for "the nicest manipulation" in 1892, is still practised in jobbing foundries, though in high-volume work automated moulding lines and, since the 1990s, 3D-printed sand cores have largely removed the need for it. The mercury practices described alongside it have not survived: fire-gilding, in which an amalgam is brushed on and the mercury "driven off by the application of heat," is now banned or abandoned almost everywhere as lethally toxic, and mercury has been driven out of thermometers, barometers and mirror-silvering. The 2013 Minamata Convention, in force since 2017, commits its parties to phasing out mercury mining and most mercury products; Almaden in Spain, the greatest mine in the 1882 figures quoted here, stopped production in 2002. The safety warning at the head of the page is not an exaggeration: mercury vapour causes irreversible nerve and kidney damage.
Written for this edition, 2026.