How to cut a Nobby..polishing of rough opal made to look easy…
Watch master cutter Justin from Black Opal Direct polish a piece of rough ‘Nobby’ with a flat colour bar into an oval cabochon. In this video Justin gives 12 tips to cut and polish a better opal.
Justin begins by showing you the ‘nobby’ to be cut.. it has a rare pattern. Crossed between a ‘pinfire and palette pattern’ Justin happily calls this one the ‘galaxy pattern’.
What is a flat colour bar?
This stone has a flat colour bar. Justin explains if you ‘grind or loose the cabochon dome you will loose the colour around the edges’. This is called a ‘fried-egg look’ where you have the colour only in the centre of the stone and you have worn away the colour bar edges.
In order to keep the stone looking like a cabochon you ‘simply round the edges of the stone’ thus making the stone look like a cabochon.
- Remove host rock. Using a texter draw a line around the stone to where you want to cut. Use this as a guide whilst slicing the opal on the slicer. Justins’ handy hint is to make sure you remove your blade every time so it doesn’t rust’.
- Upon fixing blade fill well under slicer so the blade is wet.
- Rest arms and hands on block so that you are steady. Go gently – if you push you will wreck your blade and it will wear out quicker. Let the blade do the work. If you gently guide the opal you will discover the blade will do the work and the blade will last longer.
- Rub opal on wheel with water. Work around the edges of the stone.
- What opal cutting wheels do I need? – Justin begins with 320 Grit -‘ this is quite rough..it removes potch or opal very quickly’.
- 600 Grit – work stone around for the right shape. Justin reminds you that the ‘slower you go the less likely you are to make mistakes…if you are not sure about something STOP…study it .. a timely reminder that in polishing it’s not about how many pieces or how fast you can polish them.
- THINK– if you go in and have a hack at a stone that’s when you can make mistakes. Opal is a softer material than some other gems. Once a colour bar has been polished it can not be returned!
- Dop Stick- how to put an opal onto a dop stick. In detail Justin explains the technique. From carefully selecting the correct dop stick to the use of heat and wax to getting the stone to sit flat.
- 600 GRIT NOVA WHEEL- shaping the opal to a perfect oval shape. Importance is placed upon looking down onto the top of the stone so you get a good idea of the stone’s shape. This wheel removes all the scratches, lumps & bumps from the stone which are a result of the harder cutting wheels.
- 1200 GRIT NOVA WHEEL – the aim of this wheel is to nicely polish the stone and to check that the dome of the cabochon is nicely rounded. Every surface needs to be polished so that all scratches are removed.
- Felt wheel with Cerium Oxide – the final polish. The importance of keeping a ‘wet well’ and painting ‘Cerium Oxide’ onto the wheel is discussed. Further handy hints on polishing can be obtained from ‘maintaining a good polish on opal’.
- Back of the stone is then polished using 600 GRIT WHEEL.
12 tips to cut and polish a better opal is a great tutorial based video to ‘wet your appetite’ and get you on your way to polishing like an expert.
Beginner opal cutter package available from www.blackopaldirect.com