and thoroughly dried, or a thin coating of collodion, which is also dried.  The screw is placed in the ordinary polishing triangle and the flat face at a polished on a tin lap with diamantine and oil.  In polishing such surfaces the thinnest possible coating of diamantine and oil is smeared on the lap—­in fact, only enough to dim the surface of the tin.  It is, of course, understood that it is necessary to move only next to nothing of the material to restore the polish of the steel.  The polishing of the other steel parts is done precisely like any other steel work.

[Illustration:  Fig. 36]

The regulator is of the Howard pattern.  The hairspring stud is set in the cock like the Elgin three-quarter-plate movement.  The richest finish for such a model is frosted plates and bridges.  The frosting should not be a fine mat, like a watch movement, but coarse-grained—­in fact, the grain of the frosting should be proportionate to the size of the movement.  The edges of the bridges and balance cock can be left smooth.  The best process for frosting is by acid.  Details for doing the work will now be given.

[Illustration:  Fig. 37]

[Illustration:  Fig. 38]

To do this frosting by acid nicely, make a sieve by tacking and gluing four pieces of thin wood together, to make a rectangular box without a bottom.  Four pieces of cigar-box wood, 8” long by 11/2” wide, answer first rate.  We show at A A A A, Fig. 37, such a box as if seen from above; with a side view, as if seen in the direction of the arrow a, at Fig. 38.  A piece of India muslin is glued across the bottom, as shown at the dotted lines b b.  By turning up the edges on the outside of the box, the muslin bottom can be drawn as tight as a drum head.

HOW TO DO ACID FROSTING.

To do acid frosting, we procure two ounces of gum mastic and place in the square sieve, shown at Fig. 37.  Usually more than half the weight of gum mastic is in fine dust, and if not, that is, if the gum is in the shape of small round pellets called “mastic tears,” crush these into dust and place the dust in A.  Let us next suppose we wish to frost the cock on the balance, shown at Fig. 39.  Before we commence to frost, the cock should be perfectly finished, with all the holes made, the regulator cap in position, the screw hole made for the Howard regulator and the index arc engraved with the letters S and F.

[Illustration:  Fig. 39]

It is not necessary the brass should be polished, but every file mark and scratch should be stoned out with a Scotch stone; in fact, be in the condition known as “in the gray.”  It is not necessary to frost any portion of the cock C, except the upper surface.  To protect the portion of the cock not to be frosted, like the edges and the back, we “stop out” by painting over with shellac dissolved in alcohol, to which a little lampblack is added.  It is not necessary the coating of shellac should be very thick, but it is important it should be well dried.