The Crystals are shown on  different Spectrum glaze, as indicated.

All Glaze Crystals are lead-free and food safe when fired to a minimum cone 06.  These crystals are very versatile and can be used successfully from cone 06 to cone 6.  They can be used with any glaze in this firing range to produce a great variety of different appearances.  They can also be intermixed.  Many beautiful combinations of two or more colored crystals on your choice of glaze background can be used.

We recommend that the crystals be dropped or placed onto the final coat of glaze while the surface is still wet allowing the crystals to stick to the glaze.  this way you can position the crystals where you want them on the piece.  However, these crystals will run a lot when fired up to cone 5 or 6 and should not be applied near the bottom of the piece.  This is not a concern at cone 06 or 05 as they will not move and spread nearly as much at lower temps.  These crystals can also be mixed into a liquid glaze to be brushed on.  However, they have a tendency to settle to the bottom, so you will have to stir frequently.