How to determine type of finish

[Tony Hartwell]

Hi guys, I am new to this site & this is my first post, you all seem very helpful & hopefuly you can also help me, I have two questions firstly, what procedure do you use to determine what type of finish has been applied to a piece of furniture regardless the age of the piece. I know metho will soften a shellac finish & thinners will soften a lacquer finish, but what about oil, wax, varnish, polyurethane & then there are mixtures like the ones from feast watson, they have a fine buffing oil which is a combination of tung oil & waxes, maybe it takes about 20 years of trial & error & experience to know what you are doing.

The other question is about an old office desk that I have & wanted to try & find out what type of finish was used on it. I think it could be about 40-50 years old. The colour of the desk is a darkish brown & the finish appears to be on top of the wood not in the wood.

I applied metho to a side rail where the finish had crazed & found that the finish became soft & runny & then tacky, thinners gave the same result only quicker & turps had no effect at all. When applying the metho & thinners the finish that came off was brown & left the wood it’s natural colour. When I tested the top I got a very different result, thinners & turps had no effect at all, although the thinners did fade the finish a little, but when I put the metho on & scratched a bit with my finger nail some of it came off, it didn’t go soft or runny or tacky but rolled in to little balls, after I wiped off the metho & let it dry for a second or two I used a scraper to take some more off, this time a small film lifted off, it looks like an old bluster that you pull off your finger, it felt rubbery & also stretched a little, it was light tan in colour with lines in it, could be brush marks.

Ok that’s it sorry about the long read, I hope someone took the time to read it & I get some answers, also thanks to Neil for putting me onto this site & the help with my registration.

Thanks & all the best
Tony Hartwell.

[Shane Watson]

Hi Tony,

The question of why you want to know what type of finish that is currently on the desk could be more important. If you have already scraped some coating off I would imagine you plan to completely remove the old finish and repolish. If so there really is no need to know the current finish unless you want to keep it original and repolish it using the same or similar process. Regardless, lets see what I can come up with for you http://ubb.ubeaut.com.au/ubb/biggrin.gif

From my experience I would say the desk must be around 40-50 years old. Although it could be older. Ply was invented in the 30's from memory. I would say that the base would have been polished with Shellac. Probably with a light toner/stain in it to achieve a richer brown colour. Although with age and oxidisation finishes will darken. Plus not to meniton the years of dust,dirt and waxes that would have been applied. As for the top. Well it may well be a spirit lacuer/varnish which was most commonly applied with brush.

But all thats just a guess from experience. Remember it may have also been refinished a couple of times over its life...

To get back to your original question about indentifying different finishes. It seems you have already done the most common tests used anyway. There are many more though and it depends on the polisher doing the testing to what method they use. Some other tests involve igniting metho on the finish. Or just taking a small scraping of the finish and having a close look at the resulting shavings. You knocked it on the head with the 20 years experience comment http://ubb.ubeaut.com.au/ubb/biggrin.gif I have a wee way to go yet, but doing it regularly sure helps in understanding.

Actually A lot of the time the main reason a polisher might do these tests is to determine the best method of stripping. A lot of the old timers used to make up there own chemical strippers dependant upon the finish they are about strip. So they needed to be sure of the finish so they made the right brew.

Hope all that gives you something to go on. If not, it was at least something to read http://ubb.ubeaut.com.au/ubb/wink.gif

Cheers, and welcome to the B.Board!



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Shane Watson..

Combine Love & Skill & You Can Expect A Masterpiece!

[ubeaut]

G'day Tony

Welcome. http://ubb.ubeaut.com.au/ubb/biggrin.gif In most instances ethanol (metho) will also soften lacquer and lacquer thinners will soften shellac. Your piece, as Shane says is more than likely shellac on the base with the top possibly being a nitrocelulose lacquer which has had something over the top probably wax. This could explain the balling of the finish when scratched, also why the turps and thinners had no real effect other than the thinners fading the surface.

Unless the top had been refinished by an amateur I would say what looks like brush marks could also be from the grain. Most professionals would never leave brush marks on in the finish.

If you intend to get into high class restoration it is important to know the type of finish used so you can finish the piece in the same way and with the same finish as the original. To use another finish like polyurethane would not only be sacrilegious but would devalue the piece dramatically, in some instances making a very valuable piece of furniture almost worthless to an avid collector.

A general rule of thumb is: almost everything even half decent made between the 1850's & 1950's was finished with shellac. From that time on take pot luck. This is a very, very broad generalization but does help a bit.

Practise and time will help.

Cheers - Neil http://ubb.ubeaut.com.au/ubb/smile.gif

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Nemo mortalium omnibus horis sapit.

[Tony Hartwell]

G'day guys thanks for replying to my question. The finish was in bad shape so I removed it by scraping it off, worked well. The reason I wanted to know what type of finish was on the desk was so that I could learn abit about finishes & antiques on a piece that had no real value. I was really happy with the end result, scraping left some of the finish in scratches & dents so it has still got an old look but a new finish. I mixed shellac flacks as a sealer & then used a lacquer, I then rubbed with a feast watson fine buffing oil. The lacquer I use is a pylon product that I use on my wood turning, I'm not use what it is but I read in some old post about n/c lacquer, can you explain what this is.
Thanks Tony Hartwell.

knowledge is like an antique, it should be passed onto the next generation.

[RETIRED]

Gooday.

N/C Lacquer is Nitro Cellulose Lacquer, basically an industrial finish that is generally sprayed and dries quickly in the right circumstances.

HTH.

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Ian () Robertson
"We do good turns every day"

[Shane Watson]

Tony,

Mate great to hear.

If your keen on learning more about finishes etc. Take a look at one of Neils books. 'A Polishers Handbook' (http://www.ubeaut.com.au/book.html) I havnt read it myself, although knowing Neil it would be filled with good stuff.

Generally Neil said it all with the 1850's-1950's comment. That is actually how I most commonly determine the finish. If its a half decent piece then its most likely shellac. And treated as such unless it dont look like shellac and then the tests come in handy. But I usually find that if it isnt shellac, then the piece has most likely been refinished at some time. And again that is a fairly broad generalization.

Have fun!

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Shane Watson..

Combine Love & Skill & You Can Expect A Masterpiece!

[This message has been edited by Shane Watson (edited 16 October 2000).]

[This message has been edited by Shane Watson (edited 16 October 2000).]