Celluloid Repair - pits

[Glug]

Hiya Folks,

I've started messing around with repairing celluloid, and it's quite fun so far

Here's part of my 1950's Scandalli that somebody drilled 5 holes in before and after filling the screw holes:



I epoxied the holes from the inside which reduced the air leakage quite a lot.
Then I applied celluloid dissolved in acetone and waited 24 hours and wet sanded it with 600 grit wet/dry paper.
The problem is I'm getting pits in the new celluloid.
I tried repeating the process and the same thing happened, here's a closeup:



That's after I wiped it with IPA so I think the whiteness of the pits is just the lighting.

Anybody know what I'm doing wrong ?
It's possible my celluloid mix is too thick so I'm trying some thinner mix at the moment.

 

[debra]

What I tend to do is to create a mix of celluloid and acetone that become a paste with consistency like glue. I smear it on "generously" but not like a huge bulge. It needs to dry for 24 hours, then sanding and this process repeats once, twice trice... until I end up with a perfectly flat and smooth surface. Sanding starts with a relatively coarse grain, maybe a bit at 100, then 200, 400, 600, and when it's smooth but dull it's time for polishing, first with coarse and then fine grain, until you have a perfect shine and nobody can tell it wasn't factory original.
What this requires by far the most is patience and time!

 

[Glug]

Yep, I've read all your posts I could find on the subject
I've got 400 to 3000 grit, T-Cut, Brasso, and yellow and red 'rouge'.

I've made the 'glue like' celluloid and it's working fine except for the pits.
I'll give it a few more tries and see what happens, there are plenty of other defects to get rid of anyway.

 

[debra]

Yep, I've read all your posts I could find on the subject
I've got 400 to 3000 grit, T-Cut, Brasso, and yellow and red 'rouge'.

I've made the 'glue like' celluloid and it's working fine except for the pits.
I'll give it a few more tries and see what happens, there are plenty of other defects to get rid of anyway.

The pits are probably the result of air bubbles in the celluloid paste you are making. You need to do more sanding to get rid of them, and then you probably have too little celluloid left on the accordion so you need to add a new layer of paste, and repeat and repeat... but try to keep the paste free from air bubbles.

 

[Glug]

Cheers, I'll give that a try tomorrow.

I've got about 10cc of celluloid mix in a bottle so there shouldn't be a bubble problem with that.
It could be the way I'm applying it to the surface.
I'm sure some experimentation will find the answer.

Do you clean the surface with anything before applying celluloid ?

 

[Sebastian Bravo]

Are you sure these are air bubbles Paul? i think it's caused by sanding a lot, the celluloid raises it's temperature when sanding and it starts self ignition, I noticed that happened when i worked the celluloid of the Hohner Gola months ago. If you sand a lot, focused on a small part, these small white points appear...

I would sand the surface just a little with 240grit before applying the celluloid, put acetone on the surface and wait 3 seconds, then apply the celluloid mix

 

[JIM D.]

For those bubbles you can use some acetone on your finger and work it in around the bubbles. You should soften the celluloid finish to a
paint like substance to fill the holes.

 

[Glug]

Thanks for the replies.
I'm fairly sure it's not air bubles.

At the moment I'm doing the grille and the same pits are showing up, so it's time to find a fix.

I'm wet sanding with 1000 grit so it shouldn't be overheating (probably).
I've previously tried stippling the pits with acetone and it didn't work.

I just tried stippling and then drawing the surface layer with more acetone so I'll see if that makes a difference.
Which does sound like what Jim is suggesting.

 

[Sebastian Bravo]

Were did you buy your acetone? because sometimes it's mixed with other things. I tried with acetone products to remove nail paint and it worked slow with the celluloid. Then i bought pure acetone and it was great to soften the celluloid

 

[boxplayer4000]

Glug,
I would ask where you got the celluloid to make the repair.
A very experienced repairer advised me to, if possible, to use celluloid from the parent instrument. Quite often there are 'spare' areas returned round the edges of the accordion. I suspect, without expert knowledge of polymers or plastics, that celluloid has changed and evolved over the decades of its existence and there may sometimes be a possibility of mis-match.

 

[Glug]

Both reasonable questions

The acetone is "W.S.Jenkins & Co ltd" 250ml Acetone in an air tight tin from the local hardware shop. I'm sure it's 100% pure acetone or they would have been sued.
The celluloid is from CGM Musical (black celluloid sheet), I didn't spot any spare areas on the box.

I wouldn't be at all surprised if modern celluloid is slightly different from old (1950s) celluloid.

In particular there's a thing called "celluloid rot" where the celluloid decomposes over time and becomes brittle, it seems to be mainly reported in relation to guitars (and strop razors): https://acousticguitar.com/ask-the-expert-all-about-celluloid-rot-and-what-to-do-about-it/
So you would expect modern celluloid to have changed slightly to avoid that problem.

But I haven't found a report of "celluloid rot" in relation to accordions.

I am having some success at getting rid of the pits: remixing the pitted area quite deeply with neat acetone mostly works but it's about 50/50 success so far. And there's a tendancy for the pits to come back if I apply fresh celluloid in the same area.

I'm about to try mixing fresh celluloid deeply in a pitted area, ie. use fresh mix to melt the pits.

 

[Ventura]

because this is giving you a lot of pitting and problem
(would drive me mad)
i wanted to suggest a possible alternate approach for this accordion

cut out some band-aid sized patches, pre-sand the edges to a taper,
soak them until pliable, acetone-wet the area to be patched so they will stick,
apply the celluloid Band-Aid

i wonder if that might give a nicer result for you ?

was just thinking about how they put the celluloid on in the first place
(as pliable sheets, hand rubbed over the glue covered wood)

also... i guess you are being super careful to keep windows open and
no flames or sparking things like old style light switches or pilot lights
on appliances in nearby rooms

 

[Glug]

Good idea, but don't think I can do it on the grille since the celluloid sheet is 0.6mm thick and the grille celluloid seems much thinner than that.
I probably can do it on the main body though where I left some pits to be treated later.

I'm only using acetone from a couple of 5cc ish bottles (mix and neat) so the fume risk is quite low.
And I do fumer in a different room

 

[Glug]

Solved I think ...

I was trying all the options and got to dry sanding (Sebastian Bravo implies he was dry sanding) and it seems to have stopped.
Apparently acetone likes mixing with water and I think it was sucking up water from the wet sanding. Maybe if I waited longer for the 'new' celluloid to set it wouldn't happen, but dry sanding is a safer way to avoid the problem.

I'm half way through fixing the pits on the body and no new pits are showing up.
Then I'll give it a couple of days to set before I wet sand for the polishing.

btw. I found "Commandant 4 cleaner" while searching the web and it's damn good for finishing: 1500 grit wet & dry and then just polish for an hour.

Commandant 1830590 C45C Cleaner No 4 0.5 Kg : Amazon.co.uk: Automotive

Commandant 1830590 C45C Cleaner No 4 0.5 Kg : Amazon.co.uk: Automotive

www.amazon.co.uk

 

[Pipemajor]

Well done ? .Perseverance, that's all it takes!!