Knowing how thick to make the lines and how much detail will be shown is tricky. This is a letterpress plate from boxcarpress.com. In this press the characters are about 5 mm high. The stroke width is 1pt. These are Aramaic characters from the Moabite stone. The complete enclosing rectangle is about 2 1/4" by 3".
Different depths are available, we find the 0.047 relief depth (K152) is best. While shallower ones will stamp a crisper design, it will be difficult to avoid sponging pigment out of the recesses when cleaning the high spots. Traditionally polymer plates have had metal backing (and were brittle), but these are flexible and inexpensive. When designing them create a border around the outside. This is important because when the stamp is pressed hard into the clay, the edges smear outward, that containment-line keeps outside design edges clean. Also, the plates do not actually need to be stuck to a piece of wood, it is better to lay them face down on the clay and use a wooden block to press them into the clay (which needs to be quite stiff). Because they are flexible it is easy to peel them out. Use spray cooking oil as a parting agent if needed. The cost: A 2"x3" stamp cost me about $50 (with shipping) in Aug 2020. But, as I was checking out, their site informed me that the minimum charge is $35 and that I could have ordered 40 square inches more for the same price. They accept PDF and bit image files and the shopping cart enables previewing. The cart might generate CMYK plates (four of them for process color printing), just remove the CMY ones and keep the K (black). You likely will not get it right the first time. The most common mistake is having too much detail or too small printing. It is best to make your images using vector graphic software like Illustrator or Inkscape. Another common mistake is to forget to make them reverse-reading (horizontally flip them).
Boxcar Press website
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