Repair vintage celluloid

[Bernie Daniel]

Just something I played around with that might be of use to someone.

I had an old (circa '30s era) damaged albeit fancy mandolin pick guard laying around. I do not even remember how I got it. Anyway it had a large hole all the way through probably caused by the usual celluloid break down often referred to as "case rot" I'm not convinced that there is such a thing. But often this kind of deterioration is ascribed to celluloid "off-gassing" (or something else). But it doesn't matter the cause.

I was putting some amber shellac (Bulls Eye brand) as a sealer on some spruce when it dawned on me the shellac was the about same color as a lot of old celluloid. So i found that old pick guard and put a piece of tape on the back and then filled the "low area" with shellac. I place it on a flat surface and then more or less forgot about it. About 2 months later I noticed it again and the hole was filled with solid layer of dry shellac but of course there was still a big "trough" or depression because the solvent had evaporated leaving only the solid shellac. So I refilled depression with shellac and let it dry for a few weeks again. I repeated this process a few more times finally ending up with the hole being fully plugged and actually a small plateau of shellac. I then sanded/polished with 1500 grit sandpaper and then micro-mesh until level and this is the result.

It is not a perfect repair but for sure it looks much better than a hole!! I'll probably try to fill the back in with a clear epoxy to give it strength assuming it does not react with the shellac or celluloid. The result could be made to look better by picking a better color of shellac I suppose?

[George R. Lane]

Bernie,
Since the pick guard looks like wood, I would tell everyone that is a knot in it.

[Bernie Daniel]

Bernie,
Since the pick guard looks like wood, I would tell everyone that is a knot in it.

It does kind of look like a "swirl" in the celluloid.

[Graham McDonald]

The celluloid is actually disintegrating, chemically breaking down. Every film archive in the world keeps their nitrate film (essentially the same stuff) at 3°C to stop that happening and in the worst case spontaneously bursting into flame. I saw a Gibson A in a museum collection a few years ago where the pickguard was breaking down in the same way. What was coming off the pickguard as a byproduct of the decomposition was acidic and turned the frets a corroded green and etched into what was left of the spirit varnish (which was mostly shellac) on the mandolin. I would be careful with that scratchplate

[Bernie Daniel]

The celluloid is actually disintegrating, chemically breaking down. Every film archive in the world keeps their nitrate film (essentially the same stuff) at 3°C to stop that happening and in the worst case spontaneously bursting into flame. I saw a Gibson A in a museum collection a few years ago where the pickguard was breaking down in the same way. What was coming off the pickguard as a byproduct of the decomposition was acidic and turned the frets a corroded green and etched into what was left of the spirit varnish (which was mostly shellac) on the mandolin. I would be careful with that scratchplate

My guess it is won't be any more of a problem then it was in the original condition with a hole in it?

My comment about "off gassing" in the OP was made in reference to my doubt that it was the cause of the deterioration (as some seem to imply) -- it is rather, as you point out, a result of the celluloid decomposition -- and when celluloid breaks down it does release a stociometric (albeit small) amount of nitric acid.

Everything is relative but all things considered I would say instrument pick guards made of celluloid have been pretty stable -- I've had a several of old Gibson instruments with pick guards close to, or even over, 100 years old and in excellent shape. My guess is the thing that causes some of them (probably a minority?) to start to decompose over time is some impurity that was in the original components of the manufacture (either the cellulose, the camphor or the nitrating agent -- typically nitric acid in the presence of catalytic amounts of sulfuric acid to generate nitronium ions). Chemical purity in the 1800s and early decades of the 1900s was nothing like later periods. The thing that makes me say that is generally the decomposition is not over the entire pick guard but rather at some point then the process spreads outward from there.

You mentioned motion picture films --I wonder in that case part of the challenge with storage is to preventing the decomposition of the three layers of acetate film that were used to contain silver nitrate and the magenta, cyan, and yellow pigments? When you look at old "Polaroid" pictures taken in the '80s you can see that process!

[bbcee]

I just unearthed a bunch of my old lutherie & music stuff from a storage space where it had been for 13 or so years (long story - don't ask). There was a bag of binding in one of the boxes that had decomposed and completely destroyed a couple of great old footpedals also stored in the box - everything, from the electronics inside to the outside powder coating. It is a strong acid! I feel lucky the stuff didn't catch on fire, as it is wont to do.

[Bernie Daniel]

I just unearthed a bunch of my old lutherie & music stuff from a storage space where it had been for 13 or so years (long story - don't ask). There was a bag of binding in one of the boxes that had decomposed and completely destroyed a couple of great old footpedals also stored in the box - everything, from the electronics inside to the outside powder coating. It is a strong acid! I feel lucky the stuff didn't catch on fire, as it is wont to do.

Nitric acid takes a bow only to sulfuric acid so yes, very strong inorganic acid. Don't suppose you were in much danger of a fire (unless it got very hot) but certainly to the effects of acidic atmosphere as demonstrated. I have a bundle of old binding that I keep on an open shelf -- just happened to do it that way and now I'm glad that I did!

[gweetarpicker]

I've always been a little paranoid about old pickguards and would be cautious about using a partially repaired celluloid guard that has already had some deterioration in the past. It seems possible that continued outgassing might corrode the instrument's finish. A repairman could use the old pickguard binding and hardware to make an exact replica.

www.vintagefrettedinstruments.com

[Bernie Daniel]

I've always been a little paranoid about old pickguards and would be cautious about using a partially repaired celluloid guard that has already had some deterioration in the past. It seems possible that continued outgassing might corrode the instrument's finish. A repairman could use the old pickguard binding and hardware to make an exact replica.

www.vintagefrettedinstruments.com

But only if you keep it in an enclosed place.

Some amazing pics on your web site.........I can't recall ever seeing a K-2 with a double flowerpot ( although I suppose I have at some time) and that pick guard on it is very interesting. I'm not sure what pigments they added for making celluloid but that one is pretty unusual.

[Graham McDonald]

My guess it is won't be any more of a problem then it was in the original condition with a hole in it?


You mentioned motion picture films --I wonder in that case part of the challenge with storage is to preventing the decomposition of the three layers of acetate film that were used to contain silver nitrate and the magenta, cyan, and yellow pigments? When you look at old "Polaroid" pictures taken in the '80s you can see that process!

I don't think anyone can predict if your scratchplate will be stable, or the celluloid around your shellac patch will continue to decompose. I think it would be safer to assume the latter.

Acetate film is quite a different substance to nitrate film. It does not self-combust, but the acetate breaks down and gives off acetic acid - the 'vinegar syndrome' from the smell - and the film base shrinks and gets brittle. Colour fade on film seems to be inescapable and these days at least brought back during digital restoration. I have seen before and after pieces of film and the digital process is quite astonishing. I worked in the sound area rather than film at the archive and the various carriers of audio signals have their own, though often related, challenges.

[Bernie Daniel]

I don't think anyone can predict if your scratchplate will be stable, or the celluloid around your shellac patch will continue to decompose. I think it would be safer to assume the latter.....

Yes I agree it is safe to say that it will continue to decompose -- all celluloid will eventually decompose. But the rate of decomposition is highly variable. Almost certainly this relates to the quality of the chemicals used e.g., the state of cellulose nitration and the added chemicals like camphor (plasticizer) alcohol (solvent) and to the chemicals add to produce colors or textures and also to the manufacturing process employed.

Who knows how long that patch will hold up? Generally the rate of celluloid decomposition is slow (except for combustion). For this particular pick guard I expect it took at least 60 years (probably more?) to reach the state of deterioration it was in when I patched it. I would be very lucky indeed to be around even half that long to see what happens to it. Of course my grandmother lived to 106 and my Dad to 97 so who knows!

[gweetarpicker]

But only if you keep it in an enclosed place.

Some amazing pics on your web site.........I can't recall ever seeing a K-2 with a double flowerpot ( although I suppose I have at some time) and that pick guard on it is very interesting. I'm not sure what pigments they added for making celluloid but that one is pretty unusual.

The K4 was made in 1916 before the truss rod was available. That said the action is low and the playability is exceptional. I have never needed to adjust the neck angle.

The pickguard is much lighter in color than on any other vintage Gibson I've seen. It is also starting to shrink slightly and become brittle so I keep it stored separately from the mandocello. For me these old style guards always seem to be in way anyway. I usually remove them when I play.

www.vintagefrettedinstruments.com

[Jim Garber]

The earlier Gibson celluloid pickguards seem more stable than the ones from the 1930s or so. The only one I had that crytallized and deteriorated was on a EM-150 mandolin. I kept the hardware and had Paul Fox create a new one.

[Bernie Daniel]

I don't think anyone can predict if your scratchplate will be stable, or the celluloid around your shellac patch will continue to decompose. I think it would be safer to assume the latter.

Acetate film is quite a different substance to nitrate film. It does not self-combust, but the acetate breaks down and gives off acetic acid - the 'vinegar syndrome' from the smell - and the film base shrinks and gets brittle. Colour fade on film seems to be inescapable and these days at least brought back during digital restoration. I have seen before and after pieces of film and the digital process is quite astonishing. I worked in the sound area rather than film at the archive and the various carriers of audio signals have their own, though often related, challenges.

Just bumping this thread up since it has been a year and the repaired celluloid is still doing just fine.

[William Smith]

I believe the celluloid compounds in the 30's was way different from the teens and 20's ust do to most deterioration is from what I've seen more so is on 30's mandolins?