Patina

[baileyuph]

What do you do when there is little patina left in a finish and you don't even know what the finish the patina represents?  These newer finishes can be a different challenge because there are so many more different bases, solvents, and issues to confront.

Cracking and checking, which comes up on the new stuff, how does one actually verify what the finish is when the old methods do not work on them because of the solvent question?

Maybe Keith has been down this path before and has intuition?

Another finish I read about is polyester based.  Now what is that and what is the base, and to add the solvent.  Without this information how can you determine it is polyester?

You can tell I have had a week of finishing issues.  LOL

Doyle

[byhammerandhand]

I used to have a bottle of "Finish Indicator" (it's since gone bad since I rarely used it.)   It would tell you broad categories of finish by putting on a drop:
- turned blue soon - nitrocellulose lacquer or shellac
- turned blue after 30 sec or so - catalyzed lacquer
- turned amber - oil-based finish (e.g., varnish)
- didn't turn color - everything else.

This article, http://hardwoodlumberandmore.com/Articles/ArticleViewPage/tabid/75/ArticleId/20/What-is-That-Finish.aspx , lists some simple tests with solvents to get you close.

As general guidelines:
- Factory finishes before WWI  - shellac
- Factory finishes between WWI and WWII - shellac or lacquer
- Factory finishes after WWII 99% chance they're lacquer or pre-cat lacquer
- DIY (re)finishes after 1950s - Polyurethane, the ubiquitous home center product
- Custom built - could be anything from shellac, lacquer, oil-varnish blend,  poly or alkyd varnish depending upon skill of builder
- Kitchen cabinets are usually lacquer.  But there are some two-part finishes that some manufacturers used over the last 15-20 years (these are similar to the Indestructable finish, below).   Some manufacturers are now using water-borne acrylic.   It can handle some lacquer on the top, but not too heavy.


Polyester finishes, to my knowledge, are mostly used on late-model pianos.

There are some finishes, Basset has one they call something like "Indestructable" that I've seen on tables.  It sort of has a greasy feel to it.  The problem is, it's not indestructable, being no stronger than the wood underneath.   So it can dent and chip.  Also, finish repair products such as burn in and touch up lacquer won't stick to it.   So it's not repairable.  And the name makes people think they can abuse it.   I had one customer that tried to clean it with the abrasive side of a Scotch-Brite / sponge pad.    I buffed for 45 minutes before giving up that I could not buff out the damage.

In the last 11 years, I think I've encountered two of those Basset tables, one stained piece and two other pieces painted black  that blistered when hit with touch up lacquer (thankfully, one of my customers put the lacquer on and I got called in to repair.)  I also had a rustic bookcase that looked like it had roofing tar, thinned with mineral spirits and wiped on.


My all afternoon job yesterday was to clean up some walnut and teak furniture from the early '60s.   For a high end condo, I would have never guessed they were that dirty.  :o  The owners were smokers, but gave it up 30 years ago.   When I wasn't pulling up the reddish tar residues, I was pulling up reddish tar residues that had captured and held dirt and soot.  I ended up changing my 8 quart water bucket after every piece and it was so dirty, you couldn't see through it.  This was after I went through nearly a whole can of cleaning wipes that turned black.   My thought was than anyone considering taking up smoking should have been there helping me.  I gave up the thought of smoking when I was 16 and nearly vomited when I had to clean the water pot out of an ashtray in the airplane hangar where I had a summer job.

[SteveA]

Polyester is mostly used to make inexpensive furniture look expensive.  Mostly done in Europe and the solvent release is much worse than the regular stuff you are accustomed to using. For polyester spot repairs I've bought touch up kits made by Konig. They work real well especially on the black. Spraying a complete polyester finish requires training, precautions, and equipment not usually found at the upholstery shop. 

On finish repairing of lusters and colors for regular furniture a photo would help greatly with the answer.  Anyway - you can clean any surface - scuff sand, and seal in the patina with seal coat.  From there you can top coat with most products of your choice.  Always test a small hidden area before committing to the entire project.  Learn what you can regarding applying color with a pad.  For chair arm tops, crest rails, and feet it's a good technique to know,
SA