Making the Lap
While the pitch has been melting, partially fill the pail (which has been thoroughly cleaned out) with water as hot as the hands can tolerate, and completely immerse mirror and tool, standing them on their edges and resting them against the sides of the pail, so that they can be quickly reached when wanted. Have a piece of soap on hand in a clean dish. The tool and mirror should be allowed to heat through before you pour the lap.
After the pitch has been fully melted and tempered, remove it from the stove and allow it to cool slightly, as it is best not to pour boiling hot pitch directly onto the tool. Now remove the tool from the hot water, dry it, and wrap the paraffined paper collar around it. There should be enough heat in the glass to cause the overlapping ends of the collar to adhere. Give the pitch a final thorough stirring and pour it onto the tool up to the level of the collar. When it has thickened enough to retain its shape, remove the collar.
Soap the channeling tool and press the channels into the warm pitch right down to the glass, as in Fig. 27. Start at the center, and locate the first channels so that the center of the lap will lie just inside one corner of a square. This is to avoid a uniform radial distribution of the squares, and so prevent zonal rings on the mirror. Press the channels in one direction first, then press the other set at right angles.
Take the mirror from the hot water, quickly soap its surface, and slide it about on the lap, gradually increasing the pressure. The channels will be closing in now, so replace the mirror in the hot water, and go over the channels again. Follow with the soaped mirror. These steps may have to be repeated two or three times before the lap has hardened sufficiently to retain its shape. By proper manipulation, any tendency for concavities to develop in the squares can be ironed out. By the time the pitch has hardened, the lap should exactly conform to the curve of the mirror. Remove the mirror and wash it off in clear water.
Using a sharp knife, with a firm shearing stroke cut away the pitch overhanging the edge of the tool. Incline the knife so as to give a slight bevel to the lap. The knife, or a razor blade, can be used to widen any channels that may have closed in. Do this cautiously or large fragments of pitch may break out. A good width for the channels is 1/8". Flush the lap under a cold-water tap to clean off the soap and any pitch fragments, and dry it. Meltdown some beeswax in a can.
Prepare a brush for the wax: a thin stick of wood the same width as the squares, with a chisel-shaped edge, over which three or four thicknesses of gauze bandage or similar material are wrapped and tied with string. Soak this in the melted beeswax (which should be smoking hot) and draw it across the lap, covering each square with a single stroke of the brush. Two or three squares can be done on a single dipping. While the mirror might be polished directly on the pitch or rosin lap, beeswax coating gives a faster, sleek-free polish, and results in a better edge. (Sleeks, or micro-scratches, faintly visible on a polished surface, may result from coarse particles in the rouge.)
a better lap is next
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