Will nitro crack if applied over a thick layer of shellac? (progress pics)

[river]

    I know that shellac is a great sealer and works with nitro, but this is when the shellac is one or two coats thick, mostly in the grain. I had the idea to make a black pigmented shellac using activated charcoal, the stuff used as an antidote for poisoning and for detox. After testing, it looked great so I went ahead and brushed it on an alder strat body:

    The mottled appearance is because the fresh coats haven't hardened enough to sand yet. But it looks fantastic when smoothed. The reason I'd want to clear coat this is because when wet, the color is 10x darker and because shellac doesn't get as much shine to it as nitro.

    At this point the shellac is a finish, not just a sealer. So I'm wondering if it can support a coat of nitro on top. I don't mind some cracking, but I want to make sure it isn't going to crack with some light finger pressure.

 

[Cagey]

I'm curious why you'd use activated charcoal as a pigment rather than a proper black pigment. It's not like real pigments are expensive, and you've left yourself where you are with nobody knowing what the ramifications are. I mean, who uses activated charcoal as a pigment? I'm guessing it's somewhere around nobody.

But, enough ass-beating.

I can't imagine you'd have a problem with a nitro finish over that. But, its quality is going to depend very heavily on the quality of the surface you apply it to. So, you're still going to have to make sure the surface is level and without blemish. Lacquer has a tendency to shrink, so any surface imperfections will show up amplified if not now, then later.

If the thickness of the shellac is such that you're worried about something as benign as finger pressure causing problems, it might be worth it to strip some or all if it off and start over. Lacquer is brittle. But, most modern lacquer compositions are such that cracking/crazing isn't the issue it used to be.

You don't say, but are you trying to cover an old incompatible finish? If not, then you may not need the shellac at all. Also, be aware that there are dyes and pigments out there that are "universal", in that they will work with any finish composition. So, sealers, undercoats, color coats, etc. can all be forced to whatever color you want. Use the chemistry that'll make you happy, throw a million coats of clear on it, and call it a love story.

 

[river]

It's on a new unfinished body.

    As far as the WHY, well, partscasters are all about experimentation, aren't they? Sometimes new ideas turn out well, many times they don't. Maybe with clear on it it will look particularly cool, maybe it will look like any black guitar, maybe it's going to be a POS. It can always be redone. Besides, activated charcoal is similar to lamp black (soot), but it isn't carcinogenic like soot. So it's not that risky for use as a pigment and a substance I'd rather work with.

I decided to go for the clear coat. If it cracks, it cracks.

 

[Cagey]

All true. I look forward to hearing about (and especially seeing pictures of) your progress and results. We'll all learn something.