Just wanted to let you know that there's a new company called Amourya Impressions (www.amourya.com) that is making large (up to 18" x 34") stamps to go in clay/porcelain/paperclay/etc. They're even using them to cast stepping stones out of concrete! You send them the artwork, or tell them what you're looking for, and they send you a stamp.
Here's a few pieces my friend made with the stamps:
Large pottery stamps!
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