Here's a different idea.... I'm not good at the details, so maybe you or others can chime in on the hows of the end product.
Make a handprint and/or date in a mosaic out of glass tiles or beads made to use in pools. Get the sticky mesh used for such tiles, trace the hand, cut the mesh, and hot glue the stones. The plaster guys have installed tile mosaics and will know how to do that part.
Some of the people on TFP will give me a hard time for this suggestion, because I'm CRAZY over LightStreams glass. But.... if I were in your shoes, I would call them and tell them what you are wanting to do. This is an extremely friendly company that design and produce exquisite glass tiles specifically for pool and other water applications. The tiles are polished such that all edges are smooth and safe.
Ask for David Knox the designer or for Brian, his brother. Ask if they could give you suggestions on how best to do this. Here is their website:
* Lightstreams Glass Tile | Shell Beach Glass Pool Step Tile. It will take you to their Shell Beach collections which shows the pieces on the mesh that I mentioned. If you do want to order the glass, they may be willing to hand select the smaller pieces you would need and maybe even the colors (bright colors or subtle colors). Brian knows me pretty well, so if you talk to him, tell him I sent you. (I've only spoken to David once.)
Like I said, they are soooooo nice, that they may just offer suggestions without you placing an order. I would also ask what glue they use to stick the pieces onto the mesh.
You can PM me if you need more info, or would like for me to contact Brian for you.
If this is really out in left field...... maybe it will spur another creative idea.
Now that I think about it.....

I might look into this, hmmmmmm... Take care! Suz.