New varnish beading/crawling on refinished furniture [poss. silicone contamination]

Question

I am not a woodworker, so forgive me if I am not using the correct nomenclature.

I sent a few china cabinets to a furniture restorer to be revarnished. They are really old pieces, between 95 and 100 years old, and we know very little about them: we know they are probably made of some Brazilian wood, as this was my grandmother's father request when he had them made; but that is about it, we do not know which kind of wood, how it was worked, nothing...

Well, after several attempts of revarnishing the cabinets, the restorer is lost: regardless of how he proceeds, the varnish will bubble soon after applied and become somewhat granulated, not anything like the furniture looked before. As I don't understand woodworking very well, I thought pictures could be helpful, so look below.

My questions are: what could be going on? And most importantly, how to stop the varnish from bubbling on this really old cabinet?

EDIT: As Graphus suggested in a comment, I would like to add that the restorer hypothesized that the problem could be, among other possibilities, due to prolonged use of wood polishers, meaning the problem could be "fisheye".

EDIT nº2: Just to give an ending to the story, I showed all solutions brought in the answers to the restorer, who said he was not familiar with any of them and would therefore not attempt them. As the cabinets have been with him for several months, without success, I brought them back as they look like in the pictures; he refused to give me back my money...

Answer 1

This appears to be classic "fisheye", a defect caused by contamination of the surface by silicone oil. In a furniture context the chief source of this is modern furniture polishes, although there are numerous other possible sources these days. Be wary of spray polishes in general and anything that promises a wet-look shine in particular people!

This is one of the worst cases I've seen photos of as it seems to involve all the visible surfaces to almost the same level (generally the effect isn't as pronounced and/or is more localised).

Given this piece has already undergone certain expected stages in a refinish — stripping of the previous finish (generally followed by some amount of rinsing/wiping off of residues with an organic solvent or water) and then at least a little sanding — it begins to illustrate how difficult it is to remove this contamination.

Standard finishing and refinishing processes must be assumed to never be effective, you have to specifically combat it.

There are various methods used to try to remove the contamination, or seal it in. These include, but are not limited to, the following:

• cleaning with ammonia¹;

• cleaning with sodium hydroxide²;

• cleaning with TSP;

• rinsing of the surface with hexane³;

• rinsing of the surface with xylene⁴;

• sealing the surface with light coats of shellac.

Just to highlight how pernicious the contamination can be, you can use a combination of the cleaning steps, being scrupulous about how you use your wiping rags or paper towels⁵, you can do multiple rounds, AND then apply shellac and still find you were unsuccessful o_O

This unfortunately leads us to the one technique known to almost always work.

Deliberately add silicone oil
Yes, you actually add silicone oil, or a product containing it such as "fisheye eliminator", into the new finish. How this works is that it lowers the surface tension of the new finish until it flows evenly over the contamination.

I say unfortunately because although it's effective A) it of course contaminates all the application tools, which may be very difficult or impossible to subsequently clean, much more importantly B) it risks contamination of the refinisher's finishing area and potentially their entire premises⁶ C) pieces treated this way will forever need to be finished the same way, and some refinishers may actually not want to touch it as a result.

This, especially in combination with some careful spray methods, is almost guaranteed to successfully combat the problem.

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Further reading (not a comprehensive overview):
Silicone Contamination on Highland Woodworking.
Fish Eye & Silicone – or, the Problem with Furniture Polish on Popular Woodworking.
Refinishing a Silicone-Contaminated Antique on Woodweb (be sure to compare and contrast some of the feedback here with Flexner's advice).
How to Prevent and Eliminate Fisheyes on Fine Woodworking (note: partially behind paywall).

Also see the disclaimer suggested by General Finishes on this page. It starts with the realistic but depressing:

There are no guarantees with silicone - it is almost impossible to remove.

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¹ This is a risky method when it comes to wood as many wood species are affected by stronger alkalis and change colour.

² AKA caustic soda or lye. The caution related to ammonia goes double here, and in addition caustic soda solutions are extremely hazardous and pose quite a risk to the user as well.

³ This is more common in non-woodworking contexts because hexane is often used as a cleaning liquid in industrial or technical applications.

⁴ Xylene is a more common solvent in a woodworking context; this is basically the same process as the preceding one just using an alternate solvent.

⁵ A step that many get wrong; the correct procedure is to wipe once and then discard, to do the utmost to prevent cross-contamination of an unaffected area from the affected areas.

⁶ No this is not hyperbole.

Answer 2

Agree with @Graphus that this looks like fisheye caused by contamination of the wood by silicone containing polishes. Fixing it, when it's that widespread is a job for a pro finisher. You've basically got three choices of approach:

1. After reprepping the piece, use an oil based finish thinned with silicone "oil." You want someone who has done this before, who knows the right products to select, and has a sense for how much silicone is necessary. This has the disadvantage that your whole piece will end up with silicone in the wood, and every future coat/finish will have to be silicone based.

2. Remove the silicone using a phosphorous based detergent (TSP). This is a lot of work - probably as much as stripping in the first place - you have to treat all affected areas thoroughly, probably multiple times, and will then likely have to sand the entire pieces, since the washing process will have raised the grain of the wood.

3. Cover it up. Shellac and lacquer both can adhere to silicone contaminated wood if properly applied. Again, a job for a pro who has done it before.

It's a gorgeous piece - Brazilian Walnut, I think, although one can never really tell from pictures of the surface alone. Worth finding someone with experience of the problem to advise and redo the finish.