Snapping Turtle Shell Finishing

I have an 18" snapping turtle shell that I would like to finish with poly, I soaked it in a solution of borax, salt and water but as you can see- there is still a lot of scale build up.
Is there anything I can clean the shell with that won't damage the scutes, I was thinking vinegar and water?

I don't know about shells but I know vinegar is alot stronger than most people give it credit for so be careful.

I like it thataway.
Finish it. The scale build up adds character to the piece. Just my opinion.

Maybe a dremel with a soft wheel?

Try using a Pressure washer- I did a bigger one up a couple years back and i had the same concerns as you. It was a nice shell but had scales along with algae and moss residue growing on it. I was also concerned about getting the meat residue completely cleaned out from underneath as well. Didnt want want something that was going to stink or attract bugs. I ended up settling on using a gas powered pressure washer. Quick and easy ...It cleaned up the shell nice and clean and i Was able to “ flesh out” the undersides of the shell/ carapace with it to clean off all of tissue and meat mebrane as well. Let it dry out for a couple days and then finished it with a couppe coats of flat laquer. It turned out very well. I would post a picture if i knew how..