If you've even found or purchased an old rubber stamp you might find that it is almost dried out and very stiff (new rubber gives easily if you push it with a finger nail). I've even had antique stamps that were a bit crumbly make a partial recovery.
What I usually do is clean the stamp with liquid soap and a sponge to get off any impurities first. Then I clean it with a good quality stamp cleaner and a stamp scrubber. You might need to carefully use something to pick out gunk in the details -- I use a blunt embroidery needle. Once this is done I load up the stamp with stamp cleaner using my finger to work it into all of the stamp. I put lots of it on, then carefully set it aside. A good stamp cleaner conditions the rubber as well as remove ink. Depending on how beat up the stamp is I might wait 30 minutes to several hours before removing the cleaner. If the stamp is still really bad I'll repeat this several times.
Of course not all stamps can be rescued but I've had a lot of luck with this method. Note that you can avoid this fate with the stamps in your collection by storing them properly. Keep them out of the sun and keep them rubber side down on a flat surface -- I've got 15 year old stamps that are as good as new because I was very careful about this even when they lived in a hot garage for over a year.
I'd love to hear about any other stamp rescue operations and methods.
An old toothbrush can be your friend when trying to get gunk out of nooks and crannies.
Hey, this is great! Thanks everyone.
I did a rescue on some stamps that had been used in Acrylic paint. In a large jar lid I put some diluted simple green only deep enough to cover the rubber (not the cushion). Put the stamp face down and left it there for hours. Scrubbed it with a an old toothbrush and put it back to soak some more. This continued for several repeats depending on the amount and the age of the paint. Instead of a needle, I used the point of a bamboo skewer to work in the worst nooks and crannies. You will need to add a bit more to the lid as some is removed each time and some will evaporate.
Those stamps are now pristine. Glycerin may be helpful with old, dry rubber. There is a lot of it in the colorless watermark inks.
Acrylic paint rescue?! Wow. I know people love Simple Green. Did it dissolve the paint or just peel it off? Is the rubber stained?
Glycerin. Sounds familiar. Wait a minute. Is Glycerin in that Ranger ink refresher? I'm no chemist obviously, but I think I heard that somewhere.
Smearing VersaMark clear ink onto it helps too.
Check out this old thread for tips and tricks, btw if you do a search you'll find several other "discussions" on the subject as well.
The bath they mention is: 2 tsp glycerin to 1/2 cup of distilled water. Mix together and then pour into a dish and then leave rubberstamps to soak overnight. Make sure the mixture is shallow enough to cover the rubber but not the wood mounts and/or cushioning. Give them a cleaning in the morning, if still not soft enough you may want to give them a longer soak.