I was using a heavy metal tamper to force high-water-content powder (about 12%) into a wooden form to make bricks. I use snug-fitted wooden spacers against the clay itself and deliver the blows to them. It became quickly evident, that even with 3/4 inch wood, my tamper can deliver greater pressure than the mold can withstand. I then switched to 3/4 inch plywood. With the same result! A metal mold seemed to be the next step but that was going to involve considerable expenditure. And were other problems: Removing the brick after pressing it in would be very difficult, metal molds are only practical if you have a machine with both pressing and extraction cycles. Another issue was getting a good logo impression on the frog: The clay is not hard enough to pull away from the mold without edges and pieces breaking off. In the end, for making sample bricks, a plastic mold and wetter clay are a better option.
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