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Hi guys,

I just noticed these odd stains under my first couple of coats of finish on my current build. I didn't notice them before I put a couple wash coats of shellac down. I've gone after them with sandpaper, and the Carruth scraper, but they seem to go pretty deep. I had to pitch a set of sides that came out of the bender with that type of "mottling" all over them. Was it the oils in the wood? I can't figure it out. Here is a shot of 1) stains under shellac

and sanded/scraped back down to wood



Any thoughts on what is causing this, and what a good solution is?

--Jay

Probably natural. They all seem to be in the same era of that tree's life

Solution: learn to love it, or examine sets as soon as you get them and return any that aren't up to snuff. Or if it was really undetectable early on, and you needed (and paid for) an absolutely flawless set, you may be able to extract a replacement from of your supplier for free. But it looks like an otherwise great set to me, so I'd just enjoy it.

Looks like it to me.

Generally, the hotter you bend, the more "leakage" you get. Normally, can be removed by sanding and/or scraping. If that fails, try wiping with a bit of acetone, but be careful you don't end up re-staining the whole panel (unless you like that look).

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Did you use spring clamps with dipped/coated tips for your linings? I read a thread about people having this sort of problem with them.

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Good judgement comes from experience. Experience comes from poor judgement.

Like what Trevor says. Sometimes they can go what seems fairly deep. In my experience they always can be sanded out. Seems to happen more on the darker stuff...

Take a look at the same areas on the inside... If the stains are present there, sanding probably won't do you much good. Lacquer thinners or acetone might help to even out the colour. Any finish you have applied would probably need to be completely removed. If you try this, try to stay away from the bindings, or they will take on some colour from the side wood.

Interesting first round of testing. I have a test mule set of sides that exhibit the same issues, so no harm, no foul. I tried MEK, Denatured Alcohol, Naptha, and 100% Mineral Spirits (paint thinner). So far, the mineral spirits are the clear (no pun intended) winner--they remove all traces of the stain with no ring or bleaching. The others leave the typical "ring" around the stain, or any area that got wet. The mineral spirits dry with no telltale trace they were there. So, are mineral spirits OK to use under shellac (as long as allowed to dry completely?) I normally use mineral spirits to thin my Tru-Oil, so it seems like it may be a good fit. Any dangers of using the mineral spirits?? Thanks!

Many solvents unfortunately have different common names in different parts of the world. So mineral spirits, I think, also gets called turps substitute, white spirit, low odour turps. paint thinners, etc. etc.. and the alternate names mean something else in different places. I think the mineral spirits you have will be a fairly random cocktail of volatile hydrocarbons including aromatics, and has its own dangers in use (check the MSDS), but should evaporate sufficiently not to bother your shellac.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor, thanks for the help. This particular cocktail has been used to thin my Tru Oil in the past with no ill effects, so I'm going to proceed. Glad I found something that cleans well, and doesn't seem to have a drawback. I'll report on the actual results.

I'd be more concerned my guitar is growing toes!

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John Lewis
Wannabe builder owned by 2 crazy dachshunds