Letterpress plates from BoxcarPress.com. Great for stamping designs.

We find the 0.047 relief depth shown here is best (K152). Shallower ones will stamp a crisper design but K152 is better if pigment will be used to highlight the recesses. For some things it can be valuable to put border around the outside of a design so that when the stamp is pressed hard into the clay, the edges do not smear outward. These do not actually need to be stuck to a piece of wood, just lay them face down on the clay and use a wooden block to press them. Because they are flexible it is easy to peel them out. When the clay is stiff enough no parting agent is needed. The cost: In 2022 the minimum charge is $35 for about 50 square inches. 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). The most common mistake is having too much detail or too small printing. Or forgetting to make them reverse-reading. It is best to make your images using vector graphic software like Illustrator or Inkscape.

Related Pictures

Example of a logo done using a polymer plate

The buff stoneware mug is fired at cone 10R and celadon glazed. The recesses were colored with a tenmoku glaze (on bisque by painting it into the recesses and sponging away the high spots). An outer containment line on the plate prevented the outside line from smearing outward and it provided a definite profile for cut-out after stamping.

Cone 6 stoneware coffee mug with a letterpress-made stamp

Medalta Potteries letterpress stamp in a cone 6 stoneware mug

This crest was made by rolling a thin slab of clay, allowing it to stiffen, oiling it and then pressing it using a letterpress plate (and a wooden block and hammer). The plate had the oval shape containment line, so cutting this shape out on a turntable was easy. A slip was applied to the back of the slice, and because it is so thin, it softened almost immediately (because of the wetness of the slip). It was then applied and pressed into place on the leather hard mug. After bisquing, an iron oxide slip was applied and then sponged off. The clay fires buff color, but it's texture retained enough iron to stain it leather brown. For certain clays, the fired surface looks remarkably like real leather.

Letterpress plates: Design for the draft

The designs on 3D-printed stamps are most often simply extruded straight upward, at an angle of 90 degrees. This makes for poor release when stamping clay. However, the letterpress plate-making process creates a comfortable draft angle automatically, this greatly assists in getting plates to release after being pressed into the clay. That means the design submitted for plate making is what is at the bottom of the recesses. Note, for example, the enclosing rectangle. It was added as containment to prevent the outside edges of the lettering from smearing outwards. That line has a stroke width of 1pt, however as noted, that width is at the bottom of the recess. The width of the line at the top is likely 3 times that. In this press of the Moabite stone the characters are about 5 mm tall. The complete enclosing rectangle is about 2 1/4" by 3". Since I am brushing pigment into the letters and cleaning the bisque with a sponge, the depth should not be too much less than this (K152).

Making ceramic "stones that cry out"

Jesus said: “I tell you, if these remained silent, the stones would cry out.” That was my que to make these clay stones - after all, fired clay is technically a man-made metamorphic rock. I make these by the hundreds on about 20 spiritual topics and give them to people I travel with on the bus to work (my idea of “spiritual” is the seeking of credible answers to life’s ultimate questions). First, I choose a clay (my favourites are MNP or MNS, usually with stains added). Next I make the design - this can be as simple as stamping it into a piece of soft clay using a custom letter press plate. Or, rolling a slab and cutting and stamping rocks using 3D-printed cookie cutter stamp combination. Or, I form the rock using a black-stained porcelain, apply a white engobe at leather hard and when that firms up I decorate using a colored underglaze. When that firms up I finish the design by carving lines through to the black using a sgraffito tool. Next, I fire them to stoneware temperatures, 1200-1300C, and then apply a white low temperature glaze to the back and fire that to 1000C. Finally I apply a custom on-glaze ceramic decal of a QRCode and fire a third time to 800C (the code goes to a web page I make). The result is an almost indestructible rock that will cry out for a thousand years.

Links

URLs	https://www.boxcarpress.com/ Boxcar Press website They make letterpress plates (or polymer plate) stamps. Online job submission and ordering. You pay by square inch.
Media	3D Printing a Clay Cookie Cutter-Stamper Create a clay cookie cutter by exporting a vector image from Illustrator into Fusion 360, adding width to lines and extruding them to form the cutter, stamp and base

Got a Question?

Buy me a coffee and we can talk