i get asked this all the time
“how thin can i go and still call it a solid?”
after cutting tens of thousands of opals, you develop a feel for what’s ideal vs what’s just acceptable
but putting that into clear words has always been tricky for me
so i finally sat down and put numbers to it
i’ve sold over 130k stones over the years, so i pulled a sample of data on 8,679 solid cut opals and mapped thickness vs size
a few things stood out:
most commercial solid opals end up around 3–5mm thick, regardless of size
the 20–25% rule is real, but it’s a minimum survival line, not where most stones land
the biggest mistakes happen in the 5–15mm range (shortest side), where people push stones too thin
quick takeaways if you’re cutting:
under 10mm → don’t go below ~2mm for rings
under 15mm → don’t go below ~2.5mm for rings
earrings/pendants can go thinner
when in doubt → aim for ~3mm
you can go thinner… but you need a reason, and you have to be very careful cutting the profile to keep the stone stable and settable
this graphic shows where most stones sit, where the outliers are, and where things start getting risky
curious where others land on this, especially setters