Sometimes the tips are cup shaped. For these the mould is made in two sections fastened by catches or by pins set in the plaster as shown in the [cut]. The hole is made larger at bottom than at top, and at the top is a little smaller than the shaft of the pencil. A plunger that nearly fits the small end is provided. The india rubber is placed in the mould and heated. When soft, the plunger is forced down to the proper distance in the press and the article is cured. Care must be taken to give the plunger a good coating of talc, and it must be made to sit vertically. The arrangement of a cylindrical hole shown in the [cut] secures this result perfectly. As distance piece a pin is passed through the plunger.
Mould for Pencil Tips.
Cane and Chair Leg Tips, etc.—By carrying out the process just described with larger moulds and of slightly different section very convenient tips for chair legs and walking canes can be made. Such tips can be modified in size and thickness to answer as covers for the mouths of bottles, test-tubes, etc.
Corks.—These may be made in moulds tapering from top to bottom. The india rubber must be packed in with great care to secure as solid filling as possible. A plunger is used that enters the larger end and is a very little smaller in diameter, so as to descend a little way into the mould. This distance determines the length of the cork. As the perimeter of the plunger strikes the walls of the mould it cuts off almost completely the excess of rubber that has squeezed up past it. An excellent modification of the mould is shown in the [cut]. The upper part with parallel sides serves as a guide for the plunger. It is a similar extension as the one recommended to be used for the plunger in the hollow pencil and chair leg tip moulds just spoken of.
Mould for Rubber Corks.
Mats.—These may generally be made in the hot press. Designs for them in great variety may be found in cut glass and pressed glass dishes. Many of these have patterns on their bottoms that can be moulded in plaster to serve as matrices.
Cord, Thread and Seamless Tube.—By placing the mixed india rubber in a cylindrical mould fitted with piston and with one or more round holes in the bottom, the material may be softened by heat and forced out of the holes by depressing the piston. This will form cylindrical thread or cord. As it descends it may be received in a box of powdered talc and be afterwards cured. By providing the hole with a mandrel seamless tubing may be thus made. In making such the mandrel usually remains in place during the curing. Plenty of powdered talc must be used.
Skeletonized Leaves as Models.—These would form interesting models from which matrices could be made in plaster. It would be possible to produce some very pretty stamps or mats from these and similar models.