I have a sapphire that is now in crown polish after being cut at 600 and now prepolishing at 3000 - 4 corners and one end went quickly and then turned 180 for opposite end 1:1.5 and 3000 doesn’t touch it - it’s like I’m not making contact but I’m feeling contact - angle and dial indicator tells me I’m making contact but the 600 finish appears to be impervious to my 3000 - used 3000 dust with valve oil the 3000 paste - anyone seen anything like this because I’m stumped?
Did you try to back down to a 1200lap
I will try that but first going to a different lap - doesn’t make sense when other facets cut at 600 and prepolised nicely to glass on 3000.
Switched lap and all is well - no idea - polished to 100,000 - it’s like the Diamond was protecting to facet from the lap by sticking to the facet - lap was slicker than the 600 grit surface of the facet? Will put this in my X files.
Hi it is not uncommon for sapphire to be harder on one side or 2 sides than the other
I have cut a lot of Australian sapphire and come across this regularly
I have just finished cutting several African sapphires as per attached
Nice gems - beauty. Went to a Corian lap and that facet polished normally - I have noticed differences in axis on different materials - my guess is the 600 grit was collecting diamond cake and slipping on the lap but who knows - - sometimes - often there are multiple causes. Thank you for the reply and love the images!!
I have to second SydP’s comment, I have also found hard facets on sapphires, even on man made Sapphire, you can also find soft facets that cut lightning fast. Sometimes when you encounter a hard facet, try reversing the lap rotation and this do the trick, BUT be careful with pressure as the lap is now driving the stone towards the mast so pressure on the stone increases.
I’ve encountered this hard facet problem on other materials, Topaz, Labradorite are a couple that come to mind.