Dear Ann Marie:
No black “granite” (Black Galaxy included) can be technically sealed. That said, what you have is a mark of corrosion that the particular acidity of the jewelry cleaner have caused by becoming in contact with your stone's surface.
Only a proven stone restoration professional could repair that kind of surface damage.
May I ask you now to please read and e-sign our Statement of Purpose at: http://www.marblecleaning.org/purpose.htm?
Ciao and good luck,
Maurizio Bertoli
Article ID: 1351
Created On: Sat, Apr 5, 2008 at 10:22 AM
Last Updated On: Sat, Apr 5, 2008 at 12:00 AM
Authored by: Maurizio Bertoli [mail@mbstone.com]
Online URL: https://marblecleaning.org/knowledgebase/article.php?id=1351