Crocus

Put tin, as pure as possible, into a glass vessel - a wineglass does very well when making small quantities - and pour in sufficient nitric acid to cover it. Great heat is evolved, and care must be taken not to inhale the fumes, as they are poisonous. When there is nothing left but a white powder, it should be heated in a Hessian crucible, to drive off the nitric acid.

Plate Powders

(a) Take equal parts of precipitated subcarbonate of iron and prepared chalk. (6) An impalpable rouge may be prepared by calcining iron oxalate, (c) Take quicksilver with chalk, 1/2 oz., and prepared chalk 2 oz., mix them. When used, add a small quantity of spirit of wine, and rub with chamois leather, (d) Put iron sulphate into a large tobacco pipe, and place it in a fire for 1/4 hour; mix with a small quantity of powdered chalk. This powder should be used dry.

Putty Powder Or Oxide Of Tin

Metallic tin is dissolved in nitro-muriatic acid, and precipitated from the filtered solution by liquid ammonia, both fluids being largely diluted with water. The tin peroxide is then washed in abundance of water. Collect in a cloth filter, and squeeze as dry as possible in a piece of new linen. The mass is now subjected to pressure in a screw press, or between two lever boards, to make it as dry as possible. When the lump thus produced has been broken, it is placed in a crucible, and closely covered up to prevent jets from entering, and is then exposed and heated to a white heat, and ground for use in the usual way; this oxide is used specially for cements, and polishing astronomical object-glasses for astro-telescopes. The putty powder of commerce, if of good fair quality, is alloyed with about equal parts of tin and lead, which answers for ordinary-purposes, but not for polishing lenses, in which good work is wholly dependent on the quality of the powder.

Razor Paste

(a) Mix fine emery intimately with fat and wax until the proper consistency is obtained in the paste, and then rub it well into the leather strap. Prepare the emery by pounding thoroughly in a mortar the coarse kind, throwing it into a large jug of water, and stirring well. Immediately the large particles have sunk, pour off into a shallow plate or basin, and let the water evaporate. This emery is better for engraving and other purposes than that prepared at the emery mills.

(b) The grit from a fine grindstone is very efficient for a razor paste.

(c) Levigated oxide of tin (prepared putty powder), 1 oz.; powdered oxalic acid, 1/4 oz.; powdered gum, 20 gr.; make into a stiff paste with water, and evenly and thinly spread it over the strop. With very little friction, this paste gives a fine edge to the razor, and its efficiency is still further increased by moistening it.

(d) Emery reduced to an impalpable powder, 2 parts; spermaceti ointment, 1 part; mix together, and rub it over the strop.

(e) Jewellers' rouge, black-lead, and suet, equal parts; mix.

Rouge

The rouge used by machinists, watchmakers, and jewellers is a mineral substance. In its preparation crystals of iron sulphate, commonly known as copperas, are heated in iron pots, by which the sulphuric acid is expelled and the oxide of iron remains. Those portions least calcined, when ground, are used for polishing gold and silver. These are of a bright crimson colour. The darker and more calcined portions are known as crocus, and are used for polishing brass and steel. For the finishing process for the specula of telescopes, usually made of iron or of steel, crocus is invaluable: it gives a splendid polish. Others prefer for the production of rouge the peroxide of iron precipitated by ammonia from a dilute solution of iron sulphate, which is washed, compressed until dry, then exposed to a low red heat and ground to powder.

Jewellers' Rouge

A rouge suitable for fine work may be made by decomposing a solution of iron sulphate with oxalic acid also in solution; a precipitate of iron oxalate falls, which must be well washed and dried; when gently heated, the salt takes fire, leaving an impalpable powder of iron oxide.