Part 10: Rough, Rubs, and Finished Stones – Understanding the Difference

Opal cutting is a journey of transformation, turning raw, unassuming pieces of earth into vibrant gems full of colour and life. Whether you're a curious beginner or a seasoned cutter, understanding the key stages—rough opal, rubs, and finished stones—is essential to success and satisfaction in the craft.

Rough Opal – The Untouched Canvas

Definition:
Rough opal refers to opal in its natural, unprocessed state, exactly as it is extracted from the ground. It often appears as irregular, opaque chunks of host rock or potch, with only small windows or hints of colour visible from the outside. At this stage, it's a true gamble—raw potential with no guarantees.

What to Expect:
Rough opal can be covered in sand, ironstone, potch, and other host materials. You’ll frequently encounter natural imperfections such as:

• Sand and sandstone
  
• Ironstone or host matrix
  
• Surface or internal fractures
  
• Pits, divots, and natural voids
  
• Potch layers (non-precious opal)
  
• Inclusions and foreign mineral content

It's a natural rock—an earthy piece full of surprises. You need to use your tools, knowledge, and intuition to extract something valuable from what initially looks like nothing special.

Risk vs Reward:
Cutting rough opal is both thrilling and unforgiving. One great stone can make the batch worthwhile, while one hidden fracture can ruin a gem. It's a true test of patience and experience.

Cutting Yields by Field:

The percentages below are used only as a general guide. Actual yields will vary depending on the quality of the rough and your experience as a cutter. A key factor is how selective you are when purchasing rough opal. Over time, I’ve learned to buy from a trusted group of sellers and have developed the experience to judge what will cut, how to cut it, and how to maximise the outcome.

For example, my Coober Pedy material now cuts at over a 90% success rate. However, when you're starting out, you can expect lower yields. Listed below are some rough guidelines based on typical first-time buying experiences:

• Coober Pedy: More consistent, with higher yields from seam and nobby opal.
  Estimated success rate: 50–70%
  
• Lightning Ridge: Beautiful, but risky. Hidden fractures and black potch are common.
  Estimated success rate: 5–10%, often lower
  
• Mintabie: Often cleaner than Ridge material. Produces crystal opal with moderate risk.
  Estimated success rate: 30–50%
  
• Lambina & Andamooka: Very mixed quality—some stunning crystal, some porous or sandy.
  Estimated success rate: 15–40%
  
• Queensland Boulder Opal: Not about removal, but shaping around the natural face.
  Success rate: Based on face retention, not volume cut

Rubs – The Preliminary Reveal

Definition:
Rubs are opals that have been roughly shaped and lightly sanded to reveal their colour and pattern potential. They sit between rough and finished stones—giving you a much clearer idea of what’s inside, but still requiring polishing and refining.

What to Expect:
At this stage, the opal will show its direction of colour, some pattern development, and will have most of the unwanted host material removed. However, rubs are not yet calibrated or finished, and additional risk remains during final shaping and polishing.

Advantages:
Rubs reduce some uncertainty while still allowing for creativity and final decision-making. The risk is lower than rough, and the time required to finish them is significantly less.

Ideal For:
Cutters with moderate experience who want a balance between affordability and predictability. Rubs are a great way to learn how to polish and finish without the full gamble of rough.

Finished Stones – The Polished Masterpiece

Definition:
Finished opals are fully cut, shaped, and polished stones that are ready to be set in jewellery or added to a collection. They’ve gone through all the stages of cutting and now showcase their full brilliance.

What to Expect:
These stones will be domed (or flat) with a highly polished face, symmetrical shaping, and smoothed backs. All pits and imperfections should be removed or minimised, and the stone should be judged on its colour, pattern, brightness, and finish.

Advantages:
No surprises. Finished stones are ready for resale, setting, or collecting. They command higher prices because the work and risk are already done.

Ideal For:
Collectors, jewellers, and those who want to admire opals without the need for equipment or experience in cutting.

Summary Comparison

Final Thoughts

Whether you're starting with raw rough or putting the final polish on a rub, each stage of opal cutting offers its own rewards and lessons. Knowing the difference between rough, rubs, and finished stones will help you make better buying decisions and become a more successful cutter over time. As you gain experience, you'll learn to read the stone, manage your risk, and truly bring out the best each opal has to offer.