Möglichkeiten um wasserfeste kleine Kristalle zu bekommen/herzustellen etc.?

As you have already noticed, crystals grow a problem for the lay, because the water-generated crystals are almost always too soluble for your project.

Let’s get the term “crystal” away.

In the mineral trade there are “fine stone chips” which were polished in the grinding drums. There could be Lapis Lazuli for you.

In glass, you should have an opaque glass. However, in the “small knock” a lot of pointed grains are produced which is difficult to process. So you need other methods to crush the glass. As a glass bead maker, I would take a blue glass rod matching nuance and heat the glass in the torch flame until I can press it with a pliers to a flat “Lollipop”. This part is then briefly heated and immersed in water. The shocked glass crumbles to a corm size which corresponds approximately to the thickness of the flattened glass.

These brushes could then be poured into a small sealing plastic vessel and some grinding powder (silicon carbide) could be used. Then leave some water in the washing machine “carousel driving”. It’s supposed to be a five-time full-wear with a preliminary wash. Thereafter, the result is assessed and either the grinding powder is continuously washed (sieve) or, after the sealing surfaces have been cleaned, again inserted into the machine.

You could also make a glass mosaic. For this purpose, the glass rod (hot) is drawn to rods, of which sections are cut in length from the channel width. The ends of this can either be rounded off slightly in the flame (pinzette!) or also deburred in the drum grinding (as above).

Glasses from Effetre, System96 or Bullseye are suitable. Remains of Tiffany works of unknown manufacturers also work. As a burner, I would use a soldering lamp whose nozzle in the middle has a large hole, surrounded by many small holes.