It is swung around as shown in the first figure, and the stamp, previously moistened on its sides, is forced in. If the stamp is properly made it is surprising how much force may be used to insert it. If the edges of the brass swinging piece are not rounded there is danger of the composition being cut. The stamp in its brass frame is then swung back over the brass base, where it is secured by a catch. The stamp is now ready for use, as shown in the second figure of the [cut].
It is imperative that no aqueous or glycerine ink be employed for continuous work with such stamps. Common printers’ ink is perfectly satisfactory, and the work may be nearly or quite as good as that executed by an india rubber stamp.
The Post Office manufactures a pad for use with printers’ ink into whose manufacture the same composition enters. The ink retainer is a piece of fine felt, one-quarter to one-half an inch thick. This is placed in the bottom of a shallow steel mould, where it enters for half its depth into a recess that it accurately fits. The composition from old stamps, melted up, is then poured upon and around it, the mould being previously oiled. When it is full a piece of strong manilla paper, of the area of the felt only, is placed upon the bottom of the glue pad on its centre, which as it lies in the mould is its uppermost part. The paper adheres strongly as the glue hardens. Eventually it is turned out of the mould, and a pad, shown in the [cut], is produced. The dotted lines show the limits of the felt pad. The glue composition underlies, surrounds and extends outwards from the felt portion. It is found that the elasticity of the composition makes the pad much pleasanter for rapid stamping.
Composition Ink Pad.
The above description gives the clew to making any stamp of this description. The matrix may be of dental plaster, or of oxychloride of zinc cement. The mould may be built up of type of any kind.
The composition is so cheap that the stamp can be made quite thick. This gives it a high degree of elasticity and adaptability to uneven surfaces. It may be mounted by adherence upon a flat board or block, provided, if necessary, with handles. If the board or block is placed upon the composition while it is still warm and liquid, as it solidifies the board and composition will adhere with great tenacity.
All moulds or surfaces to which it is desired that the melted composition shall not adhere must be oiled.
The moulds must not be cold or the composition will not enter the fine divisions. If on the other hand they are too hot the mixture will adhere. Experience will teach the right conditions for success.
Below are given other formulæ for roller composition. The formula already given in this chapter is that used by the United States Post Office Department.