Avoiding open seams in UV cabinet


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Hello everyone

I just put a white instrument in a UV box for the first time, and I have a few opening seams on it. Luckily It's only the rib/top seam, not a joint. I've had some areas of that seam open up already with the varying temperaturen we've had because of the winter wearher, so I'm not too surprised to see it.

The instrument is a cello, the box is a 180*80*80cm growth tent with three 36W armatures inside on an on/off cycle of 4/1/4/1/6/8 hours, so that It's off at night and has 1hour cooling breaks. It's been in there for about 24 hours now.

What worries me is that one of the failing joints was across the lower block, and the rib overhang on the block is 1-2mm smaller than it was. The joint is wide open, so my thought is that it could be the the top shrinking in low humidity, pulling the rib out?

For now I have put it back in the UV, but unzipped all vents I can find and leaving the top a little open. I also put a bit of water in there.

Now, I have three questions for the hivemind: Do you think shrinkink is the cause, and should I be worried about it? Should I take it out of UV and glue it, or is it fine to leave the seams open till It's been there for a few days? And lastly, does a glass of water and open slits in the tent sound like a sufficient change to keep it from happening again?

Thanks in advance!

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Right... So you're thinking humidity as well?

I changed my mind and brought the cello with me back home. I'll let it return to normal humidity and see if the seam closes back up on its own. And then I'll check how much water has evaporated from the glass tomorrow. Should I worry about too high humidity if I have a large volume of water, or should I just get a big pool in there?

I don't know if I have a hygrometer, but I think you're right.

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You need a hygrometer and some kind of vaporiser. A glass of water or even a bucket is not going to cut it! Mark's link to David's tells you all you need to know about humidity and humidity control.

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Here in Idaho I put a pan of water with a rag as a wick mostly hanging out of the water that can evaporate. On a violin I have open seams sometimes that I leave till I’m ready to varnish . Sometimes 6 weeks . If you glue it now the shrinkage that is happening could cause a crack not on a seam . 

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16 minutes ago, Tostra said:

Right... So you're thinking humidity as well?

I changed my mind and brought the cello with me back home. I'll let it return to normal humidity and see if the seam closes back up on its own. And then I'll check how much water has evaporated from the glass tomorrow. Should I worry about too high humidity if I have a large volume of water, or should I just get a big pool in there?

I don't know if I have a hygrometer, but I think you're right.

An accurate hygrometer is a must to have, it is imperative to know the humidity level both inside and outside the UV box. If the ambient humidity level is very low I would not put anything inside the box, cello expecially, unless you have a box with a very efficient humidification system. Then, if your cello has not very seasoned wood, shrinkage could be definitive and not return to its previous dimensions even after rewetting, a problem to always be considered with cellos.

 

 

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Haven't had a chance to read it through yet, but I will have a look. I don't have the possibility to gave any active control though, so it has to be some passive solution like a tub of water.

Edward, would you not be worried about it warping if you don't glue it back in place? Would you not even take it out and let it rehumidify? I could put it back immediately, but I would like to see if it corrects itself by tonight. A tub and a rag I can do though. Can it be too humid or should I just give as much surface area to the water as possible?

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43 minutes ago, Tostra said:

And lastly, does a glass of water and open slits in the tent sound like a sufficient change to keep it from happening again?

Thanks in advance!

A glass or bowl of water will do almost nothing.

But as Edward said, increasing the evaporative surface area by having the water wick up into a towel (particularly a terrycloth one) will do a little better.

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Davide, that is good to know... I think I have one somewhere, I'll look for it. When you say rewetting, should I dampen the top? It might be a little much a little fast, especially since I can only wet the outside..? I'm just trying to save the cello right now.

I don't think It's very dry, however. Doesn't feel like it, and the weather forecast says It's 95% outside. However, the top is not as seasoned as the rest, so I am a little worried about what you're saying...

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Actually, I have one if those small ultrasound cold mist things. The mist would all stay by the bottom, but would it be better than just a bowl with a rag? It would have to be on for as long as the lights, however, and it splashes water up in the air, so I'm not too happy about the idea while varnishing

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Yeah, a wick of some sort would be a decent increase in surface area. 

I live in Denmark, we just broke back above the freezing point a few days ago, it's 3C outside right now with a good amount of melting snow and slush around. Probably not ideal varnishing weather I guess

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Just now, Tostra said:

Actually, if it's cold outside and warm inside, the humidity would be low inside, right... Yeah, I didn't think that through. I'll definitely figure that out before putting it back in the tent

Cold outdoor air hold much less moisture anyway, and once it gets to around freezing, it holds virtually none.

This has a direct effect on your indoor humidity, which is compounded by heating.

Last week we had a cold snap here, with several days below freezing, and much colder at nights. In my lounge, the air humidity dropped to 23% which is pretty catastrophic for acoustic instruments of any kind.

In short, you really need to buy a hygrometer, and stop guessing at what the humidity might be.

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Yeah I suppose I do. It's not like I'm trying to screw it up, you know, I've just never had any issues with humidity before on any of my instruments, new or old, so it's not a thing I even considered when shopping for this setup. I have a hygrometer somewhere, but not a very precise one. I hope I can find it, because everyting is still closed down here in Denmark, so buying one isn't that easy.

The box wasn't actually that hot, about 25C or so. But that's still significant. To be fair though, the wood is "used to" this level of humidity over the last few months with -15 at night, so it's not as drastic of a change as if I'd brought it from 70% for instance. I guess that's why I only have an open seam and not an open top...

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I know I can buy one online, but from amazon or ebay it's a solid 3 weeks before arrival. That doesn't help much in saving the cello. I can probably find one online in Denmark, but that's still a few days, and I'm trying to find out the best thing to do right now to not potentially ruin this cello that I've spent the last few months making... I'll get a good hygrometer, don't worry, but for now I'm just trying to decide if it's best to leave it in UV or not, to glue it or not and then how to humidify the UV tent with some passive system.

I'm sorry if I sound a little on edge. I know writing is not the best thing to do when you're stressed out, but I really don't know what to do. I have spent so much of my time making this and was just excited to start varnishing one of these days (I'm not giving it a heavy tan, just a few days), and now it seems that the top is shrinking on me... It may not even be that bad, but I would obviously like to do whatever gives it the best chance of springing back in place and staying there

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I found my hygrometers. Apparently I have two. One says +14, one says +24 in my handwriting, which means I've tested them at some point and they're both terrible. Where I found them they read 50 and 60%, with the +14 giving the highest number and not reverse, and in the room where the cello has been for the past month they read 30 and 40%. I have no idea how I tested them, but if they're that inaccurate, I'm not even sure if the reading shows the right ballpark. I'll bring them to the UV box as soon as possible though, at least they will show the differential between the two

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If they are the dial type, you can probably recalibrate these.

On the back somewhere, there should be a small screw, which controls the indicator arm.

Wrap the hygrometer in a damp cloth and leave it for an hour. Adjust the screw until the hygrometer reads 100%. Leave it for 12 hours to settle, it should now be calibrated.

At best, dial types are only accurate to +/- 8%, digital types are a bit better in this respect.

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Thank you, that's a great tip! I'll do that right away.

Now, I've had time to relax a bit and think. I observed the hygrometers in the room where the cello has been, and it seems to be dluctuatong between 20 and 30%. I put them in the UV box for a while, and it reads 20%. It's about 22C in there and It's been running for two hours now. The seam seems to be settling a little bit, and I'm starting to think that it might not be shrinkage as much as just a bad spot in the seam. 

The "best" thing would probably be to wait till It's warmed up outside to start varnishing, but I honestly don't think I could wait that long. My current plan is to see if I can align this seam tonight and glue it back, then check the UV tent tomorrow when it has been running for four hours. In case it is not too warm and dry, I would resume the tanning of the cello, but on a 2 hours on/1 hour off cycle with the extra ventilation, a bowl of water and the door unzipped in one side. This feels overly gentle and should barely even heat up I think, but of course I would stay by it a full day with a freshly calibrated hygrometer to see if the humidity drops afterall.

Does this sound irresponsible to you?

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