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Sodalite Turning color

This may be a dumb question but I could not seem to find any kind of explanation online.

When tumbling Sodalite, is there a trick to preserving its beautiful blue color? The material I have is very good…(or so I think).
If I hand polish on a diamond wheel or disk, the material will polish out with a very nice smooth sheen and the nice bright blue color with calcite veins is present.
With the same material, when tumbled or put in a vibratory tumbler, it comes out of the polish stage a much darker, almost black overall color with dark bluish veins.

So back to the saw I go with a darker piece and I cut it in half and inside is the bright blue color. What reaction is happening when tumbling to turn it a darker color???

Hi I would think it must be the polish or the tumbler itself that is dying/staining the Sodalite??

Great thoughts! You know, I thought that too.

I tried Cerium Oxide on the next batch with the same results though.
I also used plastic pellet media with the CO, instead of ceramic media that I used with the AO.
It will be a bit spendy but I am thinking about trying 50,000 mesh diamond grit, I use for faceting, for the cleanest type of polish. Even though we are blessed with very pure well water, I am also going to try using distilled water also.

It is possible that the blue color is caused by dye. You might try rubbing pieces of rough with a Q-Tip dipped in nail polish remover or alcohol to see if the color is removed.