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Polishing lab created diamond

Hi! Does anyone know what to use to polish diamond or diamond like
substance (carbon material)? In the process of faceting some material
that is possibly corrundum with carbon in it that it tests out as
diamondon a diamond tester. It is something that was lab created in
the 40’s or the time of WWII.



If it were created before WWII, it would almost certainly be
synthetic sapphire; other diamond simulants like YAG or GGG, were
invented for the laser optics industry in the 1960s.

You would polish sapphire with diamond grit. In fact you can polish
anything other than quartz with diamond grit, including diamond. I
recommend 50,000 grit for final polish, but you will need coarser
grit to remove scratches. The choice of prepolish grit would depend
on what prepolish lap you are using, as some laps embed the diamond
a little deeper than others.

Interesting that it tests as diamond, what tester are you using? The
simple diamond testers work by the principle that diamond is a great
thermal conductor and the simulants arent (except SiC). CZ is about
the worst conductor of heat there is. Corundum (Al2O3) will not
combine with carbon so that is not likely to be the reason. An
evaporated metal coating on the surface would do it. If the stone is
over 30 years old it is likely to be YAG or GGG, if over 40 years
old is more likely to be a synthetic spinel like magalox.

However, none of this will change how you need to repolish it and
that is using fine diamond paste on a suitable lap. Most people use a
metal lap to carry the diamond paste, I use a phenolic but have used
pyrophillite or copper with equal success on hard stones.

Nick Royall