Frozen Opals
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Looks like vellum embedded with opal chips.  This resin sheet is irregular in shape and can be cut or broken apart easily.  Use double-stick tapes to back the sheet or use clear drying glues to attach it to many surfaces.  Sold by weight in 8 gram packs.  Varied size pieces come in each pack. 
3.99 per pack

Ideas for using Frozen Opals: 
1.  Cut out shapes for Wedding and Holiday cards.
2.  Jewelry - earrings, pins 
3.  Cut into small squares and use as mosaics.
4.  Use wherever you want an icy look such as winter scenes.   
Acid Free. Should not be used close to heat - it may melt. 
Of course you might want to purposely melt it with a heat gun - then it's great fun!