An electrotype is a facsimile printing plate duplicated from an
original. The original may be either type, a woodcut, a zinc or a
copper etching such as a line-cut or a half-tone, or it may be a
combination of type-matter and line-cuts or half-tones.
We commonly think of electrotypes as printing plates made of copper,
but any metal which can be electrochemically deposited may be used.
Because of their wearing qualities and economy, however, copper and
nickel are the two metals commercially used for electrotyping.
Briefly, an electrotype is made by taking an impression of the
original in a plastic substance, thus forming a mold or matrix;
depositing copper or nickel on the mold; removing the copper or nickel
shell from the mold and backing it with a semi-hard metal; trimming
the metal to printing-plate thickness, and bevelling, or blocking on
wood, the trimmed plate for printing-press use.
In modern practice more than twenty-five different operations are
necessary to make a finished electrotype ready for the press. They may
be enumerated, as follows:
_1. Case-making._ The flowing of a molding compound composed of
"ozokerite," a resinol-mineral wax, onto the case. The case is of
copper.
_2. Flashing the Case._ Passing a flame over the surface of the melted
ozokerite immediately after flowing the case in order to remove
air-bubbles.
_3. Case-shaving._ The automatic shaving of the top surface of the
flowed case after the ozokerite has hardened to give it a smooth, even
surface for molding.
_4. Graphiting._ Brushing surface of case with molding graphite to
prevent the pattern from sticking to the wax mold.
_5. Molding._ Making an impression from the original zinc line
etching, half-tone or type form in the waxed case. This is done by
means of a hydraulically operated molding press.
_6. Cutting-down._ The levelling off by hand, using a sharp trowel
shaped tool, of the splurge after the impression has been made.
Flashing is also used here to remove the burr left around the letters
after the cutting down process.
_7. Building-up._ The adding of wax by hand to the blank spaces 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 shell in the bath.
_11. Deposition of Shell._ The molded case is put in the electrolytic
bath for the deposition of shell thereon.
_12. Releasing Shell from Molds._ Stripping the deposited shell from
the waxed mold by dashing hot water on it. The wax is melted off case
and used again.
_13. Washing Copper Shell._ Hot lye-water or steam is used to clean
off any wax sticking to it.
_14. Trimming Copper Shell._ Rough edges of shell outside the guard
line trimmed off.
_15. Aciding Copper Shell._ An application of fluxing medium to back
of copper shell so that tin will adhere.
_16. Tinning Copper Shell._ Tin-foil is melted on the back of the
copper shell. This is the solder between the copper shell and the
metal back, without which the metal backing would not adhere to the
shell.
_17. Backing-up._ The flowing of electrotype metal on the back of the
tinned copper shell 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
finishing.
_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. Finishing._ 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 finishing 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. Trimming._ Trimming 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.