The work is heated prior to lackering in a variety of ways. In manufactories devoted principally to brass works, there is generally a lackering stove, having a broad flat top, upon which the work is laid, completely out of reach of the dust or smoke from the fire. In some few instances a circular row of gas flames is employed, just as in gas stoves, for heating a plate, which is supported on four legs like a table; this method is very neat and appropriate.
In the absence of either of these a charcoal fire, covered with an iron plate, is commonly used, and another very clean and convenient method is to make the end of a flat bar of iron red hot, and to pinch the bar in the vice, placing the work at some distance from the heated extremity, and gradually advancing it as the bar cools.
Vessels filled with boiling water or steam are sometimes employed; these are very cleanly and suitable, as there is no risk of excess of heat. Tubes are sometimes heated in the same manner for lackering, by filling them with boiling water, the ends being temporarily stopped with corks. Small pieces not having many holes are sometimes dipped into clean boiling water, the principal portion of which is shaken off when the work is removed, and the remainder speedily evaporates. In lackering the heads of a large number of small screws, they are frequently all inserted in a piece of card, which is heated over a charcoal fire or a gas flame, and the whole are lackered at one process. In thin circular works, the friction of polishing frequently suffices to give the requisite heat, more especially when the milling tool is used.
In whichsoever way the heat is applied, the temperature of boiling water should not be exceeded, as excess of heat is liable to discolour the work by oxidation before it is lackered, for which there is no remedy but repolishing; or if this evil does not occur, the heat may evaporate the spirit so rapidly as not to allow time for laying the lacker on evenly; or it may be sufficient to cause the boiling of the lacker, and in this case the surface will present small dots, caused by the bubbling of the spirit. Should failure arise from either of these causes, the lacker may be removed for another trial, by wiping off the first coat while it is still warm with a rag moistened with spirits of wine, but to remove lacker after it has become hard, it is generally necessary either to apply emery paper, or to boil the work in a ley of pearlash and water. After the work has been heated it is wiped with a piece of clean rag, and it should not afterwards be touched with the fingers, which might communicate some trifling grease or dirt, but the temperature is generally sufficient to prevent the application of the naked hand; advantage is therefore taken of any small hole that may happen to be in the work, and a screw tap, a broach, or an arbor, is inserted to serve as a handle.
For flat works, the lacker is applied in much the same manner as spirit varnishes are applied to flat surfaces, but owing to the employment of heat the lacker sets much more rapidly, and as only a very thin coating of lacker is required, the process is generally completed at one operation. Some care and expedition are therefore necessary to lay the lacker uniformly on the work, but being thinner than spirit varnish it flows more freely, and does not require to be worked to expel air bubbles.
The lackering is generally commenced at one edge of the work, and the strokes of the brush are taken in parallel lines from side to side; the surface generally receives two coats of lacker in immediate succession, and when the works are small, the first coat is always completed before the second coat is commenced, but in large surfaces, the two coats are sometimes carried on simultaneously, the first being a small distance in advance; but this requires to be done expeditiously, or otherwise the extreme edge of each coat will be liable to dry while the other is in progress, and the surface when finished will show streaks wherever this has occurred; it is therefore the better practice to continue the first coat entirely over the whole surface at the one operation, and if necessary the metal may be reheated for the second coat.
The success of the process depends however very much upon the good condition of the brush, and its being kept uniformly moistened with the lacker. Camel hair brushes are always used for lackering, round brushes about one quarter of an inch diameter are employed for small works, and larger round or flat brushes are used for those of greater size. They should always be kept quite clean and soft. When the lacker is in frequent use, it is generally kept in a small bottle, the cork of which is perforated to fit the handle of the brush, which is thus suspended just above the lacker when not in use; in this manner the brush may be kept in tolerable condition for some time. If however the brush is only used occasionally, it is a better practice to wipe it as dry as possible on a clean rag after use, and immediately wash it in a little clean spirits of wine, which may be added to the lacker to compensate for that lost by evaporation, and the brush may then be laid by for future use. It must also be remembered that the heat of the work speedily thickens the lacker in the brush, which soon becomes stiffened, and leaves streaks on the work; This inconvenience is frequently experienced even in going over a single large surface; it is therefore a good method in lackering large works to dip the brush in clean spirits of wine, and wipe it, either against the edge of the vessel, or a central wire fixed across its mouth, before taking a fresh supply of lacker. Or if this is thought too troublesome, the brush should at any rate be dipped sufficiently deep in the lacker to cover the hairs, and then be wiped against the cross wire, to reduce the quantity and mingle the fresh lacker with that previously contained in the brush.