ss is
rinsed in pure water to remove the acid, and dried by patting with an
old soft towel, and further dried by waving through the air. A little
turpentine on a rag will remove the mastic, but turpentine will not
touch the shellac coating. The surface of the brass will be found
irregularly acted upon, producing a sort of mottled look. To obtain a
nice frosting the process of applying the mastic and etching must be
repeated three or four times, when a beautiful coarse-grain mat or
frosting will be produced.

The shellac protection will not need much patching up during the three
or four bitings of acid, as the turpentine used to wash off the mastic
does not much affect the shellac coating. All the screw holes like _s s_
and _d_, also the steady pins on the back, are protected by varnishing
with shellac. The edges of the cocks and bridges should be polished by
rubbing lengthwise with willow charcoal or a bit of chamois skin
saturated with oil and a little hard rouge scattered upon it. The
frosting needs thorough scratch-brushing.

[Illustration: Fig. 40]

At Fig. 40 we show the balance cock of our model with modified form of
Howard regulator. The regulator bar _A_ and spring _B_ should be ground
smooth on one side and deeply outlined to perfect form. The regulator
cap _C_ is cut out to the correct size. These parts are of decarbonized
cast steel, annealed until almost as soft as sheet brass. It is not so
much work to finish these parts as one might imagine. Let us take the
regulator bar for an example and carry it through the process of making.
The strip of soft sheet steel on which the regulator bar is outlined is
represented by the dotted outline _b_, Fig. 41.

[Illustration: Fig. 41]

To cut out sheet steel rapidly we take a piece of smooth clock
mainspring about 3/4" and 10" long and double it together, softening the
bending point with the lamp until the piece of mainspring assumes the
form shown at Fig. 42, where _c_ represents the piece of spring and
_H H_ the bench-vise jaws. The piece of soft steel is placed between the
limbs of _c c'_ of the old mainspring up to the line _a_, Fig. 41, and
clamped in the vise jaws. The superfluous steel is cut away with a sharp
and rather thin cold chisel.

[Illustration: Fig. 42]

The chisel is presented as shown at _G_, Fig. 43 (which is an end view
of the vise jaws _H H_ and regulator bar), and held to cut obliquely and
with a sort of shearing action, as illustrated in