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Sun tanning your instrument


MJ Kwan
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I don't see how tanning would slow production much. Not many man-hours involved, and it's not like they'd be sitting around doing nothing while instruments were in the sun. They'd be working on the next five or ten fiddles.

 

Not that I have an opinion on whether the instruments were tanned or not. Haven't seen evidence one way or the other.

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Conor,
Yes I think one can draw conclusions as to whether Strad hung his fiddles in the sun for long enough to 
get a good tan, partly by calculating his productivity and the fact that they didn't have electricity
to speed up simple jobs we take for granted. His times were not concerned with antiquing as much 
as modern times are. 

Old fidels that have not been worn down to bare wood will not have acquired a sun tan.  
Just as a new violin (Joe will disagree here but hopefully he's asleep) won't get a tan
through the varnish, and so remain quite pale under the varnish for a very long time. 
Hang a violin in a UVA room with 1kw of light for 2 months and see how even one coat of varnish will prevent
any tanning of the edges etc. 

It makes no difference what Strad did really, but if you ask me he didn't faff about with sun tanning
and wrote of the slow drying time of varnish in the sun.


 

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When did tanning of completed instruments become common practice in modern making.  I am under the impression that there was a long period of time where luthiers were using primarily spirit varnish and that the use of more traditional oil vanishes has come back to the fore in present times (or I could have chronology all screwed up) .

 

 

DLB

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The work that is most sped up by our having electricity is varnishing I think.

Without a uv box you have to wait for dry , calm weather, so I think that there would have been varnishing seasons in Cremona.

Waiting for work to be ready for varnish would not have been seen as faffing about, just the order of things. And while nowadays we expect instant results, in the old days they thought nothing of deciding to build a cathedral for example, knowing that it might be finished a hundred years later.

if you make a stock of instruments and hang them up in the white, then you finish them as you need them, or as you can.

What about all the instruments that were unfinished when the shop closed? If memory serves there were eighty or so ,about seven per cent of the total made. Wouldn't an intelligent maker have stopped making if the product wasn't selling? Or could it be that instruments were made and hung up as a matter of course, to be finished later. If I could, that's the way I'd like to do it.

Obviously I don't know what went on either, but it is so much easier to make a beautiful varnish sit well on nice golden wood than on white, and I don't think things change as much as we might think - craftsmen would have appreciated a warm golden ground then just as we do now.

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Old fidels that have not been worn down to bare wood will not have acquired a sun tan.  

Just as a new violin (Joe will disagree here but hopefully he's asleep) won't get a tan

through the varnish, and so remain quite pale under the varnish for a very long time. 

 

I have no clue what the SPF of varnish is, or how it compares to the lacquer that was used on my Collings guitar... but for sure it got noticeably tanned when I intentionally put it in the sun for a couple of days after I got tired of looking at its pasty-white newness.

 

I just put out a maple sample in the sun with some clear varnish on part of it to see what happens.  The sun's not terribly strong right now, though.

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Conor,

Old fidels that have not been worn down to bare wood will not have acquired a sun tan.  

Just as a new violin (Joe will disagree here but hopefully he's asleep) won't get a tan

through the varnish, and so remain quite pale under the varnish for a very long time. 

Hang a violin in a UVA room with 1kw of light for 2 months and see how even one coat of varnish will prevent

any tanning of the edges etc. 

 

Ben,

I agree to a degree.  There is good visual evidence that the effects of light are mitigated by the varnish. 

Whether one tans or not....artificially or not...or uses other means such as ammonia, nitrites, ozone...to tan the wood is mostly an artistic decision.

Let's look at the practical side.

An instrument that is not made and stored in a vault will have the reactions to light as part of its appearance. 

UV reactions are part of the life all instruments. The resinous materials in the spruce crystalize [well understood].  The sugars in the maple caramelize [not so well understood].  These reactions have a beginning and an end.

Beyond UV the wood reacts to the blue/violet spectrum of visible light.  This exposure results in a minor decomposition of the hemi-cellulose.  One of the bi-products of this reaction is a "yellow" color ...yellow only being a convenient but not accurate description of the color. As this reaction progresses further decomposition....often as a reaction to added humidity...produces a gray green color.  This process ...accelerated on unprotected wood..goes on for the life of the piece.

Our sensibilities are so adjusted to antique instruments that even on new work our eye expects a degree of this "yellow" color under the varnish.

If one Grounds a piece of wood that has had a sun tan the reflectivity of the wood will not be as crisp in detail as an un-tanned specimen of the same wood.

Joe

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I would be interested to hear an explanation of the optical cause of UV:

-dulling the wood

-reducing luminosity

-reducing holographic effect.

...

I have some ideas, but would like to hear other explanations first

 

Nobody seems to have taken this up, so I'll just lay out my ideas.

 

UV will darken the very uppermost surface of the wood.  Most of the desirable reflective effects come from the very first layer or two of the cells, so UV tanning will cut down on the reflectivity/luminosity of that.

 

There is also a significant fraction of light that goes further into the wood, into layers that have not been darkened by UV and are still very transparent (in fresh wood).  This light can get scattered and refracted around randomly, and come back out as a background glow.  UV tanning would not have much effect on this, so I would think this glow would decrease the contrast and holographic effects by washing out the reflections of the surface.

 

In old wood, one of the distinguishing characteristics is that it is very opaque... not just a surface darkening, but a change in the optical properties of the complete thickness.  It is my contention that this is critical for the appearance of old violins, reducing the amorphous background glow of internal scattering, without reducing as much of the surface reflections. 

 

Now what we need is to tan the instrument from the inside out.  High-powered UV Luthier Lights, anyone?

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Actually, I'm basing my theory on what I have found with wood darkened by thermal processing... the internal tanning is just a joke, and wouldn't get through much thickness to be effective.

 

There might be some interesting aesthetic effects by using dark wood, then bleaching the outermost surface with the hydroxide/peroxide method.  The problem would be to control the depth and strength of the bleaching... definitely would need some testing.

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While those photos do look nice, if you like very light color, I really don't see extreme contrast in the flames.  Then, there's the added uncertainty about the lighting, which makes any conclusions difficult.

 

I posted a photo of one of my best-looking maple backs here: http://www.maestronet.com/forum/index.php?/topic/332407-great-back/?p=673220

No sun tanning, but relatively dark wood to begin with.  That entire thread is probably worth reviewing.

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Nobody seems to have taken this up, so I'll just lay out my ideas.

 

UV will darken the very uppermost surface of the wood.  Most of the desirable reflective effects come from the very first layer or two of the cells, so UV tanning will cut down on the reflectivity/luminosity of that.

 

There is also a significant fraction of light that goes further into the wood, into layers that have not been darkened by UV and are still very transparent (in fresh wood).  This light can get scattered and refracted around randomly, and come back out as a background glow.  UV tanning would not have much effect on this, so I would think this glow would decrease the contrast and holographic effects by washing out the reflections of the surface.

 

It seems that the depth of photodegradation is partially influenced by the frequency of the light involved. 

See: http://www.treesearch.fs.fed.us/pubs/29235

(You can download the paper from this site.)

 

Also of interest is mention in the abstract and conclusions of blue light and its bleaching effect.  At one stage I did a reasonable amount of reading following various wood and varnish samples bleaching in summer sunlight.  Where I live a hole in the ozone layer results in higher UV levels than in other parts of the planet.  We also have very clear atmospheric conditions that I gather results in higher levels of blue light.  (Mike Molnar might be able to comment further on this.) 

 

There are any number of papers that consider photoyellowing and photobleaching resulting from exposure to various UV and visible light frequencies.

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It seems that the depth of photodegradation is partially influenced by the frequency of the light involved. 

...

Also of interest is mention in the abstract and conclusions of blue light and its bleaching effect.  

 

Very interesting... I hadn't known about the transition from photoyellowing to photobleaching as you go from UV to blue wavelengths.  That would make the optical problems I mentioned earlier even worse, by darkening the outermost surface and bleaching the wood below that.

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Very interesting... I hadn't known about the transition from photoyellowing to photobleaching as you go from UV to blue wavelengths.  That would make the optical problems I mentioned earlier even worse, by darkening the outermost surface and bleaching the wood below that.

 

I suspect that it's even more complex than this.

 

Length of exposure and light intensity seem to be factors.  In my case exposure of samples to summer sunlight resulted in an initial yellowing quickly followed by bleaching creating a very washed out dull look.  Yellowing was far more successful in winter months.  Some of the best results came from leaving wood on an inside window sill.  I'm not sure what might have been involved there as glass apparently reduces UV.

 

For some reason I also generally seemed to get noticeable photobleaching occurring when using a light box.  I've tried a variety of bulbs including UVA, UVB, reptile, suntanning etc..

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I suspect that it's even more complex than this.

 

Yes, probably.  Everything seems to go that way.

 

If you start with fresh, snow-white wood, that's one thing... you can't get bleaching with that.

But if you have wood that's older, oxidized, or otherwise darker, who knows what kinds of surface chemistry you have, and what various wavelengths of light might do to change it.  Thus far, I have only seen UV tannning on any of my white-ish wood, either by sun or lightbox.

 

 I haven't seen any change in my processed wood due to UV, either darker or lighter.  I have seen very rapid oxidation effects:  light orange or pink coloration when first cut will rapidly get more brown, in a period of a few hours.

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Yes, probably.  Everything seems to go that way.

 

If you start with fresh, snow-white wood, that's one thing... you can't get bleaching with that.

But if you have wood that's older, oxidized, or otherwise darker, who knows what kinds of surface chemistry you have, and what various wavelengths of light might do to change it.  Thus far, I have only seen UV tannning on any of my white-ish wood, either by sun or lightbox.

 

 I haven't seen any change in my processed wood due to UV, either darker or lighter.  I have seen very rapid oxidation effects:  light orange or pink coloration when first cut will rapidly get more brown, in a period of a few hours.

 

Interesting comments!  Thank you.

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We have observed that the surfaces are to a degree protected from photo-degredation by the ground and varnish.  Here is an example of the opposite.  This and several other violins were built around the turn of the century, set up, played, but never grounded or varnished.  Basically they hung in the shop and then the house and attic of the family of the maker.

The color of the wood is far darker than we see in the exposed areas of Cremonese instruments.  When the maple was finished with ground and a clear coat of varnish the reflectivity increased.  However when the back was tilted the flames were partially fixed in the optical phase change.

Joe

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My guess is that that's not photo-degradation, but oxidation.  If it was photo-related, I don't think the grain direction would matter, and it would darken evenly.  For oxidation, where the grain is parallel to the surface, it won't oxidize as deeply compared to where the grain runs more steeply at the surface.  I think the deeper oxidation/darkening depending on grain direction would cause the partial fixing of the flame.

 

For the old violins that started life with varnish, you don't get the oxidation for a long time until the varnish wears off.  Even then "worn off" might not be completely so, as perhaps there's still something plugging up the grain to prevent oxidation... sweat, dirt, French polish...

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