HELP! blotchy soundboard

Byrolinda · Post by **Byrolinda** » 17 Apr 2008, 08:21

I have stripped my soundboard using a scraper and fine sand paper. 2 problems remain. There are some small brown 'spots' where rust has dripped from the old strings (is it possible to bleach these ?) and, despite 3 days' work, there is still some lacquer in the grain giving a blotchy appearance when I wiped it over with meths. Any thoughts on how to get a better result? Arthur Reblitz makes depressing reading on this subject!

Tom Tuner · Post by **Tom Tuner** » 17 Apr 2008, 18:35

Oxalic acid solution can be used to lift rust without distressing the wood further. One wonders what happened to cause rust to drip on the sdbd. Methanol will probably not satisfactorly remove the finish. If this is an antique the finish is doubtless shellac, which will come off with ethanol or aqua ammonia. If the finish is actually nitrocellulose "gun cotton" lacquer it will require actual lacquer thinner, containing acetone among other things, or something like methyene chloride, providing that hasn't been banned.

Post by **Barrie Heaton** » 17 Apr 2008, 21:25

Depends who white you want the soundboard as Tom as stated OA used hot is vgood at removing rust stains.

Hydrogen peroxide is very good at bleaching the wood the 2 part system is best but be warned all them liquids add moisture to the board.

Barrie,

Byrolinda · Post by **Byrolinda** » 18 Apr 2008, 20:28

Thanks to you both. I have gone down the ammonia route (a pretty smelly experience!) Things look SO much better! The rust spots have faded considerable with the application of a few dabs of bleach. There has certainly been a damp problem at some stage, though not severe enough to affect joints, veneer, etc. There are 'spots' of damp as if the inside of the piano has been 'drizzled' on. I wonder whether it's been in the line of fire of a soda syphon, or spraying champagne!
I'm thinking of adding some whiting to one or more coats of the varnish, just to iron out the remaining minor blotches.

Tom Tuner · Post by **Tom Tuner** » 22 Apr 2008, 17:30

You didn't tell us what it that you are working on (I found out from Piano World). In restoring historic or antique instruments the general rule is not to use materials that are going to seriously compromise the authenticity of the piano. Your idea of using varnish that is loaded with filler is not too appealing. You don't want to obliterate the grain under a cloudy finish that will not look at all appropriate on a vintage instrument (unless you want it to resemble one of Kimball's horrible 1980's grands which appear to have a coat of semi-opaque 'stain-killer' under the varnish). The original finish was almost certainly shellac. I hope you noted whether it was orange, blond, or white, and use the same in refinishing. Fe+++ (rust) stains are insoluble and generally have to be chemically reduced to Fe++ to be removed. Hydrogen peroxide of 20-volume strength will decolorize wood (if it doesn't eat it up), but is somewhat dangerous to work with. Cellulose sponges and natural bristle brushes may spontaneously combust. Citric acid will also lift rust stains to some extent.
Keep in mind that the piano is 120 years old. You won't make it look bran-new no matter what. Some blemishes may be considered "beauty marks og age".