Points from June McKenzie's very interesting and useful talk at our March General Meeting  on Selection & Preparation of Stones for Cabochon Competitions:- 

• Know what stone has been nominated for the competition

• Select your material carefully

• Choose only the best quality stone
• Look at it closely- when wet, dry, in good light, at all angles. Use a 10 X magnifier
• Note any flaws, chips, etc
• Lay template carefully to avoid the flaws, etc. then mark outline carefully
• Cut with trim saw. Allow a bit around edge as a precaution
• Check again with the 10 X. to see which side is best for front face?
• Note : Stripes in a stone are best if they are placed diagonally across the cab.

GEMSTONE MATERIALS SUITABLE FOR TUMBLING
Stones of similar hardness can be tumbled together:
Group 1
Agate of all types	Bloodstone
Chalcedony	Chrysoprase
Carnelian	Beach Pebbles
Jasper	Petrified Wood
Group 2
Amethyst	Aventurine
Sodality	Tiger Eye
All Quartz group	(Rose, Green, Canary, Milky, Rutilated, Citrine, Smoky, Clear)
BUT Opal, Malachite and Rhodonite - each should be tumbled separately
Rhodochrysite is very soft and should not be tumbled with harder materials but it can be combined with Goldstone.
Other stones suitable for tumbling:
Amazonite	Chert
Lapis Lazuli	Prehnite
Opalised Wood	Abalone Shell, Aragonite