The best erasers I have found for carving stamps are Mon Ami brand. They are available in the office supply department at Kmart. Almost any high-polymer drafting eraser will work nicely, but these tend to be expensive. The traditional Pink Pearl and Rubkleen erasers are fine for simple designs, but won’t take a lot of detail. They are too springy for very fine carving. Some larger art supply stores carry Factis brand erasers in a variety of interesting styles. There is a white kind that comes in a useful large size, as well as some beautiful translucent and fluorescent ones. I have tried a few of these and they seem to work well. I recommend that you not bother with Magic Rub, in spite of the wonderful name. They are frustratingly soft and flexible, as well as having an odd, bubbly texture. They are difficult to carve and will drive you insane.
The first step is to find a design you like. You can simply draw yourself a picture in clean black and white. Or you can lift graphics from almost anywhere. I particularly like to carve alphabets. The letterforms are generally simple shapes that are quick and pleasant to carve. Of course, if you get really ambitious, you can use whatever elaborate pictures you can find. Use a photocopier to enlarge or reduce your image to the exact size you want your stamp to be. Or you can print it out, though this may reduce the image quality. Make sure the image will fit on your eraser without having bits of it disappear off the edge!
Using tracing paper, carefully copy the outline of the image. The tracing should extend only as far as the edge, and no farther. Be as precise as you possibly can—this is why I recommend a mechanical pencil. It is almost impossible to get a good tracing using a dull pencil. Do not press too hard on the tracing paper. The groove made by excess pressure on the pencil point will make transferring the image difficult.
Turn the pencilled image upside down on the eraser and rub it firmly all over with your thumbnail, thus transferring the loose particles of graphite from the paper to the eraser. It is important to transfer the whole image before lifting the paper. You can hold down one end while you lift up the other to see if you have missed any spots. When you have done this, you will have a reversed image on the eraser, and the pencil on the tracing paper will be slightly lighter, though not gone. If you want to have a pair of stamps that are mirror images of each other, you can trace on the back side of the tracing paper to reverse the image, then transfer as usual. This is particularly useful for dingbats, printer’s ornaments, pointing hands, etc.
The Exacto knife I use is a standard No. 11. As far as I can tell, it is not necessary to have any special or unusual blades. Just make sure the blade is sharp and the tip is not broken off. If you have been using your knife to cut paper or cardboard, change the blade before carving any stamps. Cut the outline first. With the blade about 1/16 inch deep into the surface of the eraser, follow your pencil line exactly. Angle the blade slightly to avoid undercutting. After the outline is finished, cut any internal pieces. These can be angled more sharply if necessary, to make removing the pieces easier. Once you have cut along all your lines, begin trimming away the background. Some kinds of erasers are very easy to trim, while others have a tendency to tear, thus destroying important parts of your design. Work slowly and carefully.
After you have trimmed away all the superfluous rubber, it is a good idea to clean up the outside of the background. If there are any areas along the edge that might pick up ink and print, trim them a little lower than the rest of the background. Now try a test print of your new stamp. It should look exactly like the black and white original you started with.