Stiffening spruce with UVA

[lamanoditrento]

In NK Forstners's "the luthiers blog ebook" there is mention of spruce being stiffed with exposure to ultra violet light:

"Years ago I read an article in The Strad that said UVA stiffens spruce (the samples were around 2mm thick) by 10%. If they are 10% stiffer, you can make 'em thinner. Spanish makers hang their work in the sun to get a tan."

I haven't been able to find the Strad article referred to and my googling hasn't found any other reference to this idea.

Anyone have any ideas about the veracity or any other info about this at all?

[simso]

If I get a chance I can test it out for you, I have high intensity uv lights here, suntan on your skin in around 6 seconds, red skin in around 30 seconds.

I also have low UV lights and specific spectrum uv lights, like 365nm.

Steve

[kiwigeo]

I've heard that propping your top wood in front of a copy of Penthouse open at the centrefold page gets the wood really stiff

[blackalex1952]

I have high intensity uv lights here, suntan on your skin in around 6 seconds, red skin in around 30 seconds.
I also have low UV lights and specific spectrum uv lights, like 365nm.

...like, what are you smokin' man?

[blackalex1952]

Actually, all jokes aside, I'm very interested in UV tests if you want to and have time. I am also interested in any comments from people who have tried torrefied wood. There is a respectable Aussie supplier investigating the possibility of setting up a torrefaction kiln here. An expensive process using inert gasses and serious control of the humidity and temperature, along with the expense of "cracking the code" without cracking too much material, I believe.-Ross

[Crafty Fox]

There was a TV program many years ago on Australian violin makers, on ABC or SBS, and I seem to recall Harry Vatillioso hanging either the top or back plates on his washing line.
I think the program was called "The Box That Sings", about 15 years go. I think?
I don't recall the purpose of the hanging but perhaps its related to stiffening?

[simso]

..like, what are you smokin' man?

Many years ago, I use to inspect and certify aircraft for defects, non destructive testing.

One of the methods of inspection was the use of fluorescent dyes for finding cracks that fluores under specific lighting conditions. Still have all my equipment from those days.

Steve

[blackalex1952]

Many years ago, I use to inspect and certify aircraft for defects, non destructive testing.
One of the methods of inspection was the use of fluorescent dyes for finding cracks that fluores under specific lighting conditions. Still have all my equipment from those days.

I know you are a busy man, but as I said, it might be a great experiment. Perhaps if it actually showed some tangible results, it would be akin to torrefaction at a fraction of the cost. There are probably some test results of this kind of treatment somewhere, an interesting question.

[Bachiano]

Here is a pic of Marcelino Lopez Nieto's workshop with tops hanging under a skylight.

Last year I saw one of his guitars ( spruce top ) it was brand new and I could not believe it.
The patina on the top looked like it was at least 50 years old.

Now whether this stiffens the top is a different question.

Credit for photo goes to Orfeo Magazine #3 Pg.55
https://issuu.com/orfeomagazine/docs/orfeo_3_en

[Mike Thomas]

A couple of pictures of a violin I made a some years ago. I hung it out in the Hobart sun for a few days, purely to get some colour. The last picture shows the contrast between the tanned back and an untanned offcut from the same piece of maple. Quite a difference after only a few hours in the sun. This is commonly done by violin makers, largely to provide a more golden ground for the varnish. Whether it improves the sound of the violin is debateable, but it certainly appears to do it no harm.