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sun tanning


MANFIO

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I think it would be fair to say that the long pattern is both longer and narrower. In actual measurements, the numbers aren't huge, but the total effect of narrowing AND lengthening makes a big visual difference.

And yes, it's true that it was totally abandoned in the late 1690s. Unlike other patterns that he used, discontinued, and then reused later on, I can't remember EVER seeing a re-use of the long pattern once it was discontinued. If there is an example, maybe someone else will point it out.

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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.


Are you implying that the effect of sun tanning at "cellulose fibers" level is similar to what the "long pattern" does in a violin?

The article is from the March 2000 issue of Strad. It is more of a quantitative analysis. The experiment basically applies a certain type of ground or treatment to the wood, then measure the difference for before and after. It did not really explain how and why the treatment work in such way. I did not feel comfortable to follow the data so blindly.

However, I did tan the inside of my last (and first) violin. I did not like the color achieved at the time. I thought it is kind of unnatural looking. Well.. that was before I did the varnish. During the varnish process, I saw how the taning can do to the visual effects. I now have second thoughts about the coloring process. I think I will try it on the outside this time.

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Well, I was trying not to imply anything until I had some historical facts and Michael has now provided those (thanks Michael).

I mentioned earlier that the effect of the sunlight in crosslinking the cellulose fibers would be greater across the grain than in the direction of the grain and that the effect would also be more pronounced on Spruce than maple.

This, in turn, would mean that the stiffness of the wood would be increased across the grain, though not in the length.

'Stiffness' is a carefully defined engineering parameter and relates directly to other factors such as resonant frequency.

So all this leads me to two possibilities but I have not yet thought through which is more technically accurate.

One is that it was Strad's normal practice to toast his violins in the sun before varnishing (we know he did it after varnishing) but then he tried to save time by avoiding this step only to find that he needed to lengthen and narrow the belly slightly to bring the lateral and longitudinal stiffnesses back to where they had been before.

The second option is the opposite; that he normally only exposed the varnished violin to the sun and experimented with exposing them in the white. The same criteria apply i.e. that the ratio of width to length would need to be altered to compensate for the changes in stiffness.

Whichever way round it was, he abandoned it either because the visual appearance was less satisfactory or it was more time consuming.

Italy is the most southern of the European violin making areas and certainly the country with the most sunshine, so it is quite reasonable to suppose that sunlight played a bigger role in violin making than just the effect on varnish.

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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 [CUT]

One would need a dedicated team of photochemists and photophysicists with a passion for violins.


Glenn (oops! Sorry Daryl!), when you said this:

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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.


I assumed there must be some sort of literature documenting these effects on wood. There is plenty of research done on wood that has nothing to do with violins. :-) I'd just like to understand the basis for your statements. Specifically, I want to learn more about "dimerizations, photopolimerizations and molecular rearrangements" which occur in wood with "high energy photoexcitation provided by UV light". :-)

Manfio--what about the wood on the Messiah said "new" to you? Does it seem very light to you? Reflective? Sparkly? Clean? Thanks!

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Michael, yes there is a slight difference. The one that I left in the window is slightly darker and I find it more attractive. However, I left it in the window for the entire summer(4+ months), and the one in the light box for about 6 weeks. I'm afraid I wasn't very scientific about it. I can't say for certain if the quality of tanning from the lightbox is equal to that of sunshine, but I've had some experiences with leaving violins hanging outside that I can avoid with the lightbox. The lightbox is also 24hrs/day and is somewhat climate controlled.

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Andres, my comment was not specifically related to effects in wood but in general relating to the science of photochemistry. Most people forget, or never knew, that photochemistry i.e. photoinduced chemical reactions, is a branch of science in it's own right.

My own research was the study of certain photochemical reactions in vapor and liquid phases (alas not in wood) and they are reactions totally unlike chemical reactions that might take place in a test tube.

We think of light as being a 'mild' sort of phenomenon. In fact, light has the power to excite molecules into excited states where they behave in ways unimaginable to the regular student of chemistry.

I am now involved in the manufacture and sale of holograms so quite a way from photochemical research, but this thread has given me the idea to see if any serious work has been done on light induced changes in wood.

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Maybe Daryl hold the key to your question.

It would be nice to have two rib pieces from the same wood and check their stiffness to make sure they are the same. Then toast one with UV and see if the the stiffness has changed. (The stiffness would be measured accoustically by resonant frequency).

My prediction is the that the one exposed to UV will have a different (greater) stiffness.

We don't know how Strad tuned his plates but I think expert luthiers can feel the stiffness by flexing the plates as they work them. So, my thought is that wood (especially spruce) that has been uv cured, would have subtly modified stiffnesses along and across the grain and this would call for longer and narrower dimensions to achieve the same 'feel' as uncured wood.

Maybe Daryl can tell us how deep the brown coloration goes in his test pieces. I think sooner or later, and certainly with wetting, the color would penetrate quite a way.

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Glenn, are you familiar with early photographic techniques? The reason I ask is that I've always wondered whether the Cremonese makers had unwittingly used some pre-photographic process in there varnishing phase. I'm referring specifically to the Gum Dichromate technique.

If you "sensitize" your vioin with a mixture of potassium dichromate and gum arabic; "expose" the violin to the sun using the refractory rays off the wood grain as your "negative"; and then use alum as a stop bath/hardener you've basically reproduced some elementary photographic processes.

Michael, what do you think? I recall a article in a VSA journal about there being chrome in the Cremonese varnish.

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Maybe Daryl hold the key to your question.

It would be nice to have two rib pieces from the same wood and check their stiffness to make sure they are the same. Then toast one with UV and see if the the stiffness has changed. (The stiffness would be measured accoustically by resonant frequency).

My prediction is the that the one exposed to UV will have a different (greater) stiffness.


You don't have to predict. That result is already given in the Strad article.

Actually, my second thoughts about tanning the white violin was inspired by Daryl's photo of a tanned neck.

As to wetting the wood, I have some reservations about it. It may raise the grain and cause other unplaned effects. But I will certainly give it try with sample pieces.

I have been planing to make a UV light box. I was thinking to use mirrors instead of aluminum foils for maximum reflections. After reading this thread, it makes me wonder if the glass in the mirror will actually filter out the UV before reflecting the UV. Does anyone have any idea?

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Rats. I need to get hold of that article quickly and save myself some effort.

So what did it say relative to the uv effect on frequency or must we keep guessing?

Since my last note, I plugged uv, wood, aging into google and there is a lot of research about it largely related to the concern over the effects of uv on decking. Aparently the effect of uv on lignin (major component of wood) is well documented so I need to dig into that a bit more.

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Ispirati,

Aluminum foil is dirt cheap, easy and quick to apply, doesn't weigh anything, etc. When you apply it all wrinkly inside the box, it will scatter the light around randomly and (I assume) fairly evenly throughout the box. The advantages of using aluminum foil are many, and I can't think of any disadvantage.

The advantages of using mirrors are unproven at best and probably non-existent, and seemingly offset by higher cost, weight, and complexity of construction. Additionally, I don't regard it's "accurate" reflecting of the light to be an advantage at all, compared to the wrinkly scattering of aluminum foil.

Bottom line is my light box will dry mastic varnish in a few hours of exposure, and it uses simple, somewhat wrinkled aluminum foil applied to the inside of the box with 3M 77 spray adhesive. I'm not sure how much better you expect a mirror-lined box to perform.

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Well, my violin is inside a plastic bag round the clock, it rained some days and it seems it's getting still more darker. Perhaps the cycles of humidity (rain) and dryness (sun) plus the long exposition are helping to get a good tan. But I do find it strange when I see it under the rain...

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Yes, most plastic blocks UV, however most glass does not, so if there needs to be protection, use glass.


"So I figured the only thing that could really hurt your eyes (bright light can never hurt your eyes) is ultraviolet light. I got behind a truck windshield, because the ultraviolet can't go through glass, so that would be safe, and so I could see the damn thing [the first atom bomb detonation]."

(Richard Feynman, Surely you're joking, Mr Feynman, p 116-117)

A different glass formulation?

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