It is very important to apply properly the ground which is used to protect the glass from the action of the etching fluid. The surface of the glass must be thoroughly clean and absolutely dry otherwise the wax will not adhere properly to the glass surface causing spreading of the etching fluid under the wax. It is also important to make sure that the coating is as thin as possible. This can be ensured by heating the molten wax to make it thinly fluid, but taking care against burning which can be prevented by heating the pot with the wax in an oil bath. A temperature of about 250'F. will be high enough. It is also advisable to heat the glass piece to about the same temperature as the wax or to keep it immersed in the melt until it acquires the same temperature as the molten wax. The following are two simple formulae that will produce a firmly adhering coating on glass which willnot flake off during the drawing of the lines. Melt 2 kg. of white beeswax and add to it 25 g. of pale powdered rosin, a lit
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