Author Topic: Nitrocellulose problem  (Read 253 times)

hermv2000

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Nitrocellulose problem
« on: August 12, 2018, 12:30:49 PM »
I am applying a finish on a curly maple corner cupboard.  I have used this method on various project for many years .  Water based aniline dye stain, followed by one coat of BLO, then several coats of shellac
followed by one coat of low luster Nitrocellulose lacquer to kill the shine of the shellac.

I work in an air conditioned shop but open the doors and run a ventilation fan to expel the air when I spray lacquer.  The weather has been warm and rather humid the past few weeks.

I waited a day before applying the shellac, a fresh mix made from just purchased flakes.  The next day the shellac sanded out fine, no gumming up on the sandpaper, just a fine powder.

The following day I applied one coat of low sheen Nitrocellulose lacquer.   

The next day I noticed a bit of blushing in a few areas.  Over these areas I used a rattle can of Mohawk blush retarder, as directed.  The blush seemed to have disappeared but 18 hours later the retarder has left the lacquer in the areas
treated quite soft.  It won't sand, gumming into balls when I try that. 

So now I have a mess and need help.  I tried a quick wipe with lacquer thinner to see if that would remove the retarder but that brought the blushing back with a vengeance.

Stripping it back to bare wood is not an option.  There are too many shaped surfaces such as the glass door mullions. 

Any help will be appreciated.

Herman

R Bohn

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Re: Nitrocellulose problem
« Reply #1 on: August 16, 2018, 11:42:35 AM »
Hi Herman
Got your email asking for help.

 You didn't say if this is an antique or a new piece. If it's new water based dye stain is OK. And I mean just OK. Water based dye will not penetrate finish residue from stripping. I seldom use dyes because they are not as uv fast and are not easy to reverse. Alcohol/oil stains will work better.
 Next the BLO under a film is a major mistake. Myth is that it pops the grain. The drying time for BLO could be a couple days or in humid conditions maybe a few weeks. BLO will fill the pores and limit the bite of the shellac. Could cause finish adhesion problems in the future. I have seen 100's of test boards on this and the result is that most every liquid will pop the grain, just some are better for finishing wood.
 Shellac in humid weather could take a day to dry, before re-coating. And I let the shellac dry at least 3 days in dry weather before top coating with lacquer.


 Lacquer on antiques seldom looks correct and is only used on tops for added durability. Adding lacquer on a antique corner cabinet is added time unless that's the look your going for.


So when you used the retarder, it melted all this stuff together. At this point, and I haven't seen the piece, I would wash the piece with lacquer thinner and try to remove the BLO.


If your using BLO and not mixing paint, Your research material is out dated
Most restorers miss on the colors, different styles have distinctive looks/ colors.  If your working on an antique and it doesn't look like an antique when your finished, you loose!  I didn't see any toning/ shading in your procedure. When working on a piece it helps to have a picture of an original to compare/copy.
Randy


 
Restoration and Conservation of Fine Antiques Serving Museums, Dealers and Private Collectors Nation wide since 1979

hermv2000

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Re: Nitrocellulose problem
« Reply #2 on: August 16, 2018, 01:47:14 PM »
Thank you Randy.  It is a new piece.  I'm done with linseed oil, won't try that again.  In my reading on using it I've seen both pro and con arguments.  But even highly regarded craftsmen like Al Breed admit to using it under shellac.
WRT water based dye, yes, I have experienced fading on a piece I did many years ago, it occurred while exposed to sun.  Now I only use such dyes on maple, everything else in cherry or walnut is not stained.

I have let the piece sit for nearly a week and it's beginning to harden.  I'll let it sit for another week and see what happens.  Otherwise I'll carefully scrape off the lacquer and wash it with thinner.  If it gets hard I'll give it a very thin coat of nitrocellulose to even out the sheen and then call it done.  I'll post a photo when I'm done with it.
Herman