From Xylographs to Lead Molds; A.D. 1440-A.D. 1921 Part 3

_7. Building-up._ The adding of wax by hand to the blank s.p.a.ces in the molded case so that in the finished electrotype they will be well below the printing face.

_8. Black-leading._ Making the face of the molded case electrically conductive by applying graphite.

_9. Stopping-out._ Insulating with a thin coating of wax the edges and back of the copper case to prevent copper being deposited except on the face of the mold.

_10. Pumping-out or Oxidizing._ Coating the face of the molded case with chemical copper to hasten deposition of copper sh.e.l.l in the bath.

_11. Deposition of Sh.e.l.l._ The molded case is put in the electrolytic bath for the deposition of sh.e.l.l thereon.

_12. Releasing Sh.e.l.l from Molds._ Stripping the deposited sh.e.l.l from the waxed mold by das.h.i.+ng hot water on it. The wax is melted off case and used again.

_13. Was.h.i.+ng Copper Sh.e.l.l._ Hot lye-water or steam is used to clean off any wax sticking to it.

_14. Tr.i.m.m.i.n.g Copper Sh.e.l.l._ Rough edges of sh.e.l.l outside the guard line trimmed off.

_15. Aciding Copper Sh.e.l.l._ An application of fluxing medium to back of copper sh.e.l.l so that tin will adhere.

_16. Tinning Copper Sh.e.l.l._ Tin-foil is melted on the back of the copper sh.e.l.l. This is the solder between the copper sh.e.l.l and the metal back, without which the metal backing would not adhere to the sh.e.l.l.

_17. Backing-up._ The flowing of electrotype metal on the back of the tinned copper sh.e.l.l for the purpose of making a foundation for printing (electrotype metal is an alloy of 94 per cent lead; 3 per cent tin for flowing and 3 per cent antimony for hardness).

_18. Scrubbing the Cast._ A power operated scrubbing machine using a hydro-carbon oil as the cleansing medium to clean the printing face of the electrotypes.

_19. Cast-sawing._ Sawing off the surplus metal of the cast before finis.h.i.+ng.

_20. Flattening the Casts._ Hand operation with mallet and flattening block to take the warp out of the electrotype caused by the contraction of the metal in cooling.

_21. Rough-shaving._ Planing off superfluous metal from the back of the electrotype.

_22. Finis.h.i.+ng._ Putting the printing surface of the electrotype in perfect condition for press after leaving the foundry department. This is done by hand and requires a high degree of skill.

_23. Smooth-shaving._ The finis.h.i.+ng shave of metal from back of electrotype to bring it to the required thickness.

_24. Routing._ Cutting out the high but non-printing surfaces of the electrotype by a routing machine.

_25. Guard-line Sawing._ Cutting the guard lines or bearers off the electrotype to practically the finished size before blocking or bevelling.

_26. Blocking._ Fastening the plate on wood base with brads driven through the metal.

_27. Tr.i.m.m.i.n.g._ Tr.i.m.m.i.n.g the wood mounted electrotype to its exact finished size.

_28. Type-high Machining._ Used for planing the bottom of the wood base so that the mounted electrotype is of printing press requirements, i. e., .918" high.

ELECTROTYPING BY THE LEAD MOLD PROCESS

Electrotypes made by the genuine Dr. Albert Lead Mold Process are always duplicates of fine-screen half-tones or mezzo-tints used for the highest cla.s.s of commercial job-work, such as three and four color process or duo-tone printing on paper with a highly glazed surface.

The largest press used in lead molding will give a maximum pressure of two thousand tons per square inch on a thirty inch ram hydraulically operated. The weight of this press is over thirty thousand pounds.

[Ill.u.s.tration]

In the lead mold process the plastic medium used is a soft thin sheet of what is called "impression lead," .040 inches thick, instead of wax, and the lead is placed on top of the original to be duplicated, instead of vice-versa, as in the wax-molding process. No "building-up"

nor "black-leading" is necessary.

In all other respects the consecutive steps towards the completion of the lead mold plate are identical to those used in the Wax Mold Process.

ALUMINOTYPES

The age long progress in the development and perfection of typographical printing surfaces, from the period of Xylographic blocks on through the successive inventions of individual movable cast-metal type, stereotyping and electrotyping, by both the wax and lead-molding processes, reaches its culmination in _Aluminotypes_.

Briefly, it is a method of casting printing plates of aluminum alloy in molds made from a composition of plaster-of-paris. In its essential points it is a modern adaptation of the process credited to William Ged of Edinburgh in 1730 and afterwards modified and improved in the early 19th century by Earl Stanhope of England.

In practice, the original to be duplicated is placed on a molding-slab. A molding frame is set upon the slab and enclosing the original. A special kind of oil is then sprayed on the face of the original. This is to facilitate the release of the plaster mold so that it will not "tear" when it is ready to be lifted off the original after solidifying, and at the same time to retain the sharpness of the mold.

The molding medium of plaster composition in a semi-liquefied state is then poured on to the original in the molding frame. The surplus plaster is sc.r.a.ped off flush with the top of the molding frame.

After the plaster matrix in its molding frame has set sufficiently it is released by means of cams from the working pattern on the molding-slab.

The plaster matrix is then placed in a drying oven, through which a forced draft of hot air is kept circulating at high pressure. The thorough drying of the mold takes approximately ninety minutes.

When the plaster mold has become sufficiently dried, a round hole is cut through the bottom of the matrix in an offset of the molding frame. This hole is the gate through which the molten aluminum is forced. The mold is then securely locked upright in a specially designed casting machine.

The Aluminotype is cast by pressure and not by pouring as in the case of stereotypes, which depend entirely upon gravity. Fused aluminum alloy is poured into a hopper on the casting machine. A piston operated by the agency of compressed air forces the aluminum evenly into all parts of the plaster matrix.

When the cast is completed the molding frame is taken from the casting machine and the Aluminotype removed from its plaster-of-paris matrix.

_AUTHORITIES_:

"An Outline of the History of Printing," by R. A. Peddie.

"Typographical Printing Surfaces," by L. A. Legros.

"Manual of Electro-Metallurgy," by Napier.

"The Encyclopedia Brittanica."

"Electrotyping and Stereotyping" Typographical Technical Series, Vol. XV.

The Rapid Electrotype Company.