I made my stamp on a POM tea glass (is anyone else saddened that POM no longer comes in those?) so that it could be a roller stamp. For a flat block, a piece of wood or even a milk lid would work wonderfully.
REMEMBER! WRITE BACKWARDS!
It took a couple tries to get the numbers even and without any blobs in the middle but fortunately, the glue can easily be peeled off.
For these I used acrylic paint but it worked just as well with an actual ink pad.
I also had the idea of making stamps using foam shapes but I don't have any. Guess I'll do that another day. I'll also have to try using veggies as stamps like I keep seeing on Pinterest. Those always have such neat results. Anyways, I hope you make some awesome stamps and make some adorable creations!