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sun tanning


MANFIO

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For the first time I sun tanned a violin till it got a golden brown hue. It took some months, it's time consuming, but everything in violin making is time consuming, am I wrong?

I had to keep an eye on the sky and sometimes I had to phone home to ask someone to rescue it from a tempest.

For the next violin I'm thinking about putting it inside a transparent plastic back, with some holes in it's lower part, to allow air circulation. It will protect the violin against rain, bird craps, polution, flies, etc. In this way the violin can be kept outdoors round the clock, accelerating the process.

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Well, how did it turn out? Were you satisfied with the results? Did your instrument look better because of having done this, compared with instruments where you didn't do this?

I carved most of the outside arching of my 2nd violin a few months ago. I stopped working on it for a while to do other things. I unpacked enough of my tools last night (since I've got nothing else to do for the next month until I move) to finish it, and did a lot of carving on it so it's nearly done. I noticed a very substantial yellowing on the several months' old surface compared to the newly carved surface. I think the yellowing looks very handsome. I'm very tempted, when I finish this, to let it hang in the sun for a while before varnishing it. But I don't know, I may be too impatient when it's finally done.

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Well, I've forgotten to say that I've done that with a violin in the white. Yes, I'm very satisfied with the result, the colour of the sun tanned wood will make achieving a final colour easy.

The wood gets a colour when exposed to the air but when you expose it to the air and to the sun you get a golden brown colour, the same colour you can see in your old violin wood.

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Yes, most plastic blocks UV, however most glass does not, so if there needs to be protection, use glass. I noticed that the very thinnest (extremely dilute--like ten drops in a small glass of turpentine) amount of oil on the wood hastens the coloring. Another thing that works--though I don't do it, my partner does--is to lightly dampen the wood once a day, using a plant mister. He uses a UV box, though--I don't know if sunlight would work the same.

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I have had several white Chinese instruments hanging in my shop for about year.Just varnishing 2 of them now and the wood color is beautiful!.As Manfio says it will make coloring much easier.

I think I'll try misting them with water as Michael mentions. I have some old wood here that got some water spots on it some years ago from a leaky roof during rain--the areas that got wet are extremely brown and seem to get more so after each year compared to the surrounding areas, I wonder what the water does to the wood.

Michael, any recommendations on the type of oil to use with the turpentine?

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Bob, It's all a question of degree. A uv/vis spectrum of ordinary window glass shows absorbtion starting to take place at about 400nm (the short wavelength end of the visible spectrum). The absorption continues to increase down to about 350nm where it is strong.

This is why you will burn from IR behind glass before you tan but some UV is getting through (hence the curtains and pictures fading although visible light can cause fading of pigments).

If you want short wavelength UV, below 350nm, you need to go to quartz glass which is still transparent down to almost 280nm. These short wavelengths are very damaging to organic molecules and cause skin cancer so they would do a quick job of polymerizing the terpene oils in wood turning them brown.

So, the browning will take place behind ordinary glass or plastic sooner or later, but it will take a long time.

An airy, open room sheltered from the rain but where morning and afternoon sun can penetrate (like Strad's tower) would seem to be ideal

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HongDa, you hit the 'submit' button just before me.

The water, by swelling the cellulose fibres, will allow greater penetration of the UV light and, by the way, the darker the surface, the greater the absorption of UV (white is reflecting) so your dark water spots will continue to darken exponentially faster than the surrounding areas.

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I think it must be special glass.That's why one has to be careful buying cheap sunglasses,....if the glass is simply dark it causes the irises to open more and let the dangerous UV in----kind of tricking the eyes.From this I guess most glass lets in quite alot of UV?

Concerning my post above and my violins which have been hanging indoors---they have tanned nicely albeit over about a year period.So what else is it besides the UV light I wonder...........

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Sorry to be picky, Michael, but the effect of UV is most certainly not just to hasten oxidation. There can be photo-oxidations (which usually yield colorless products), but the major reactions of interest to luthiers are dimerizations, photopolimerizations and molecular rearrangements and they do not happen without the high energy photoexcitation provided by UV light.

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Quote:

are dimerizations, photopolimerizations and molecular rearrangements and they do not happen without the high energy photoexcitation provided by UV light.


Not sure if I'm reading correctly.But how does one explain the darkening of the inside of an instrument hundreds of years old without much UV light?

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Glenn,

I recalled one of the Strad article had a comparison of differnt types of wood treatment: Sun light, UVA, Ozone, heat, Protein glue, Sealer varnish, and water soaked.

The results from UVA and Sunlight exposures were similar but not the same. It did not really explain the cause of the differences. It may be caused by the addition of UVB in sun light. Both seems to reduces damping in the wood and increase frequency. However, the transient time decrease for sun light but increased for UVA.

I am not an expert at UVs. But as I recall from reading UVA is not as harmful as UVB. Where UVB is the wave that causes damages to our skin and accelerates aging. Feel free to correct me the details if I am wrong. I just remember there are something different about the different wave lengthed UVs.

Now here are my questions:

1. Is it possible that the type of UV that causes aging to our skin can also accelerate wood aging?

2. What is the process in UV exposure that would cause decrease in the damping and increase in frequency?

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Thank you all for the input!

I know that the plastic bag would cut part of the rays but on the other hand I would get a long period of exposition.

I believe that oxidation is responsable for the effect too, and I had already noticed that moistened wood gets dark over the time.

Michael, what's the quantity of turpentine to the 10 drops of oil?

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Andres, I haven't read enough of the right kind of violin literature to know how well these effects are documented although Ispirati makes a reference to some interesting work. The problem is that it is fiendishly difficult to do the necessary experiments to evaluate scientifically all that's going on in light or UV induced ageing. One would need a dedicated team of photochemists and photophysicists with a passion for violins.

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I'd be very interested to see that 'Strad' reference if you can recall how long ago it appeared.

I'm not sure what is meant by damping, frequency and transient time but it isn't hard to hazard a guess.

At the risk of boring everyone, here goes.

UVA, which lies just beyond the violet in the visible spectrum, causes ageing of the skin by crosslinking the collagen strands thus making them less supple.

UVB photons are shorter wavelength than UVA and therefore more energetic. They cause nasty effects like skin cancer by interfering with the DNA in our cells and so they don't function correctly and I don't think this form of uv need concern us further.

I would suspect that the UVA which stitches together the collagen in skin, does the same thing to the cellulose fibers in wood. Just as the skin became more rigid and less supple, the same would apply to the wood. In effect, the stiffness of the wood has been increased which would lead directly to an increase in it's resonant frequency.

Furthermore, I would predict that this photoinduced increase in frequency would be greater across the woodgrain than in the direction of the grain.

Now you've got me really thinking about this, I can see that the effect of the UV on wood will not only produce the coloration that Manfio was looking for, but will also have an effect on the accoustic properties of the wood, especially the spruce which is less uniform in density than maple.

There is a whole topic for research here!

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I think it's difficult to assess the importance of oxidation in wood's appearance. Some say that the look of old violins is due to wood oxidation, but when we look at the Messiah (I had the oportunity to see it under the sunlight) and other well preserved violins the wood under the varnish appears quite "new".

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Manfio, I'll try to overlook the comment about the newness of Messiah's wood (in the interest of not stirring up controversy) but if I can contribute nothing to the entire Pegbox forum, I will at least convince the readers of this thread that the subject is not 'oxidation' but 'Sun Tanning' which means the effect(s) of sunlight AND THAT IS NOT THE SAME THING.

The chemical and physical processes are different and therefore it is quite reasonable to suppose that the musical consequences are also different.

In fact, Manfio, your seemingly innocent topic has caused me so much brain ache that a new theory might emerge from it but, before I expound further, I need some input on Strad's long pattern design.

Is it correct that the so called 'Long pattern' Strad is both longer and narrower than his 'normal' design or is it just longer?

Also, is it true that this 'long pattern' was something of an experiment during part of his career and was definitively abandoned at some point?

The connection with 'sun tanning' may become apparent depending on the answers.

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