Synthetic sponges are made of plant fiber (cellulose) and used in making lithograph plates and in printing.
It is important for them to be soft because they come into direct contact with the plate surface. At the same time, they must have large pores to hold sufficient moisture.
In lithography, synthetic sponges are used for various purposes such as applying platemaking solution on to the plate surface, cleaning the gum Arabic on the plate, and supplying moisture to the surface of the plate during printing. Therefore, a number of separate sponges must be prepared for use with gum Arabic solution and etchants, and for platemaking and printing, etc. The same sponge should not be used for multiple purposes. Using the same sponge can result in the mixing of chemicals which may cause problems during printing and damage the plates.
After use, squeeze excess moisture out of the sponge and leave it to dry in a well-ventilated location so that it does not become moldy while it is stored. When dried, the sponge hardens so it should be soaked in plenty of water before it is used again. Those available commercially are mostly sold in the dry state, so they should be soaked in water before use too. Sponges are consumable items and should be replaced if they become old and start to crumble, etc.
Synthetic sponges can be purchased at art supply stores that handle printing supplies.