OK I left the guitar for another month to see what would happen.
And I was pretty pee'd off after what seemed to be a disaster.
Cracks definitely all stabilised - nothing more.
Decided today to bite the bullet and sand off the cracked Nitro. But looking at it - the cracks are really kind of cool . I'm a geologist - they look quite like some cracks I see in rocks ... often filled with shiny stuff .
Which got me thinking .... what have I got to lose ?
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Filled with a gold paint.
Seems to have worked. Interesting finish.
Question is ... which finish do I coat it with now ? I'm guessing stick with nitro as there will still be some on guitar.. but not sure.