Learning opal cutting? Avoid common beginner mistakes like cracking, scratching, poor shaping, and safety errors. Read our troubleshooting tips for better results.

Avoid the Heartbreak: 7 Common Opal Cutting Mistakes Beginners Make

Learning to cut opal is incredibly rewarding, but the path from rough stone to polished gem has a few potential pitfalls, especially for beginners. Making mistakes is part of the learning process, but knowing the common ones can save you time, frustration, and potentially valuable opal! Here are 7 frequent beginner opal cutting mistakes and how to avoid them.

Mistake 1: Insufficient Water / Overheating the Opal

• The Problem: Opal is sensitive to sudden temperature changes and friction heat generated during grinding/polishing. Cutting without enough water causes heat build-up, which can lead to cracking (thermal shock) or “burning” the surface, making it difficult to polish.  
• How to Avoid: Ensure a constant, generous flow of water over the opal and the wheel/lap throughout the entire process (except perhaps final dry polishing checks). If the stone feels warm to the touch, stop and let it cool in water. Use lighter pressure, especially on finer grits and during polishing.

Mistake 2: Skipping Grits or Not Removing Scratches Fully

• The Problem: Each grit size is designed to remove the scratches left by the previous, coarser grit. If you skip a grit or don’t spend enough time on one stage, deeper scratches remain. These will become glaringly obvious during polishing and are very hard (sometimes impossible) to remove later without going back several steps.
• How to Avoid: Be methodical. Fully work the entire surface of the stone with each grit. Before moving to the next finer grit, clean the opal thoroughly and inspect it carefully under strong light (magnification helps) to ensure all scratches from the previous stage are gone. Patience here pays off immensely at the polishing stage.

Mistake 3: Cutting the Opal Too Thin

• The Problem: Trying to maximize the colour spread or chasing a thin colour bar too aggressively can result in a stone that is too thin. Thin opals are fragile, difficult to set in jewellery, lack depth of colour, and can sometimes appear transparent or ‘dead’ from certain angles.
• How to Avoid: Aim for a balanced cabochon with a reasonable thickness and a gentle dome. Assess the thickness of the colour bar in the rough and plan your cut accordingly. It’s often better to sacrifice a little bit of spread for a more durable and vibrant stone. Don’t grind the back excessively thin unless specifically aiming for a calibrated stone for a bezel setting (and even then, proceed with caution).

Mistake 4: Undercutting the Girdle

• The Problem: Grinding too much material away at the base of the dome creates an undercut girdle (where the widest point is above the base). This makes the stone very difficult, if not impossible, to set securely in a standard bezel setting.
• How to Avoid: As you shape the cabochon, consciously maintain a slight angle inwards from the widest point of the girdle down to the base, or keep the girdle edge relatively straight/perpendicular to the base. Check the profile frequently as you grind.

Mistake 5: Poor Dopping Technique

• The Problem: If the opal isn’t securely attached to the dop stick, it can shift or even fly off during grinding (dangerous!). If it’s not centred or level, it’s much harder to cut a symmetrical shape. Using too much wax can make clean-up difficult. Overheating the opal during dopping can also cause cracks.
• How to Avoid: Clean the back of the opal before dopping. Use the right amount of properly heated wax. Ensure the opal is centred and pressed firmly onto the dop until the wax fully cools. Gently warm the stone (don’t overheat!) before applying it to the wax.

Mistake 6: Rushing the Polishing Stage

• The Problem: After spending time shaping, it’s tempting to rush the final polish. This often results in a hazy, dull, or uneven finish, failing to bring out the opal’s true potential brilliance and colour play. Tiny scratches missed in sanding become very apparent.
• How to Avoid: Consider polishing as important as shaping. Keep the lap charged with the right consistency of polish (like thin cream). Use light, even pressure and keep the stone moving. Take breaks to clean the stone and inspect the polish under different lighting angles. Be patient – a good polish takes time.

Mistake 7: Neglecting Safety Precautions

• The Problem: This is the most serious mistake. Failing to wear proper eye protection can lead to serious eye injury from flying chips. Cutting without adequate respiratory protection exposes you to silica dust, leading to the incurable lung disease silicosis over time.  
• How to Avoid: Never compromise on safety. Always wear appropriate wrap-around safety glasses or a face shield. Always wear a well-fitting respirator mask rated for fine dust (P2/N95 or better) when cutting or grinding, even with water. Ensure good ventilation. Treat safety gear as the most essential tool in your kit.

Learning from Mistakes:

Don’t be discouraged by errors! Every opal cutter makes mistakes, especially when starting. Analyse what went wrong and adjust your technique for the next stone. Consider joining a local lapidary club or online forum to learn from others. By being aware of these common pitfalls and focusing on careful technique and safety, you’ll steadily improve your opal cutting skills and enjoy the process even more.