The rubber is of two parts.
1.) The pad of absorbent material, to which the Oil or Seedlac is applied.
2.) The cover, which contacts the work.
The pad need be no larger than palm size, the working part must be smooth with no creases, like a mushroom. The cover is made of a lint free cloth such as linen, and is smoothed over the absorbent pad. Not more than a teaspoon of oil is "started" through the cover by banging the pad onto the work. It is advisable to make pads for each finishing medium (Red Oil, Seedlac, etc.).
A rubber should not be left lying on the bench where it can dry out, the material in it will soon congeal and it may not be possible to restore the rubber. Rubbers should be stored in air tight, screw top jars, one for each finishing medium. Occasionally a few drops of the correct thinner should be shaken into the container to keep the rubber moist - check rubbers weekly to avoid drying out. This precaution is essential if the rubber is not to be used again for several days.
It is a good plan to work up a stock of rubbers, so that an operator is not faced with the problem of starting a fresh job with a completely new rubber. A practical way of doing this is to remove the outer layer of absorbent material of a rubber after a job has been completed and replace it with a new piece.