Regarding doing custom stamp. You need a very crisp black and white
image. If not a photographic image, like a velox, make sure you draw
with very opaque ink on very smooth card stock. You don’t want ragged
edges. But most important, try using a copy machine and reducing your
image to the actual size that you want. If it doesn’t read well in a
photocopy, it doesn’t have much chance in a stamp.
If your stamp is too complicated and you want a .8mm high stamp, for
instance, it might not read well. Also, if you have positive and
negative elements, you’ll have to experiment with the “openness” (sp?)
of your design. Sometimes when you reduce an image down, the open
areas all but disappear.
I sincerely hope this adds some food for thought and leads to some
experimenting because it is a rather expensive mistake to get back an
unusable stamp. The stamp companies follow your size specifications
and use your artwork so the responsibility to troubleshoot your design
is completely in your hands.