INDIA RUBBER TYPE MAKING.
India rubber type are often used to set up different inscriptions in
wooden handles, or different date figures in rubber stamps. The latter
are in such cases made with slots or recesses to receive them. Rubber
type are much shorter than regular type, and as a rule are larger in
the body in proportion to the face of the letter. Where only a few are
required the following process is the simplest way of making them from
mixed rubber sheet.
The type which are to be copied are set up on a level base or imposing
stone, and quads or spaces are put between them. High quads and spaces
should be used; otherwise they should be pushed up until even with the
shoulders of the type. After oiling the faces a matrix is produced
exactly as described for stamps. Before it has set quite hard the
plaster or cement is cut off so that it will just fit within a little
“flask” or frame.
The latter may be made of tin or wood and may be rectangular or
circular, provided it is large enough to include within its area the
full working face of the matrix. It should be about half an inch or
five-eighths of an inch deep. Its object is to prevent the softened
india rubber from spreading, so as to secure the requisite height of
the type produced.
[Illustration: INDIA RUBBER TYPE MOULD.]
A piece of wood or metal is cut so as to fit closely within this frame
like a plunger. It is provided with shoulders or cross pieces, so as
to limit the depth to which it can be inserted. It will be seen that
when matrix, flask, and plunger are all put together a complete mould
for a block of type is produced, as shown in the illustration, the
matrix with its plate forming the bottom of the box. After the flask is
placed upon the matrix it is filled with the mixed uncured india rubber
sheet. As a matter of preference thick sheet is used, but scraps of all
shapes can be employed as it all fuses together. The mould and matrix
are of course first well dusted with talc powder. The plunger is put on
and the whole is pressed. Heat is next applied in a vulcanizer or hot
air chamber, such as the flower pot arrangement, or in boiling water.
As the sheet reaches the boiling point 212° F. (100° C.) the flask is
removed and the plunger examined. If it goes down to its seat without
expelling any india rubber more of the latter is required and is
accordingly inserted, the plunger being taken off for the purpose. The
softened gum should ooze out around the sides of the plunger. The whole
is again put under pressure, and the platen is screwed down, and if all
is right an excess of rubber showing itself, the whole is put in the
hot chamber, the heat is raised to 284° F. (140° C.), and is maintained
there for half an hour.
It is almost a necessity to secure the matrix plate to the bottom of
the flask. This for a single operation may be done by screws, or for
several operations by hooks or catches.
When the curing is complete the mould is removed from the vulcanizer,
is allowed to cool and is opened. The block of type will come out
with perfect reproduction of the letters upon one side. If all the
directions have been followed as regards distance pieces, level
imposing surface, etc., both faces will be exactly parallel, and any
number of other blocks can be reproduced of exactly the same height,
not necessarily from the same matrix, although one good matrix can be
used many times.
The type have now to be cut apart. This is done with a sharp knife
which is kept wet. It is worked with a sawing motion, and if sharp and
properly used will cut with regularity, and smoothly. Type with knife
marks on the sides are always unmechanical in appearance and seem to be
“home made.”
The object of using high quads and spaces or of pushing them up, will
now be evident. It secures the evenness of the general face of the
block of letters, which otherwise would have a deep depression between
each pair of letters. If the quads and leads are properly arranged, the
letters will project upwards from a smooth, plane surface.
The dealers in rubber stamp maker’s supplies sell special steel moulds
for the purpose of making them. This does away with all necessity for
making matrices, and making up a flask, etc. The general manipulation
is that given above. Where many are to be made the regular mould is by
all means to be recommended.
Sometimes type are made by cementing single letters made by the stamp
process upon wooden bodies.