Tanning wood before varnishing

Posted on | September 18, 2011 | 1 Comment|

In the workshop I use UV lights to tan my instruments before varnishing and we also use UV light to dry the varnish on the instruments.  Last week I was replacing some old bulbs in my UV light box.

At the light supply shop the owner was interested why I needed these UV lights.  After talking for sometime about violin making & varnishes he thought he could provide a better UV  light for tanning the wood and offered to run a test for me.  This was a man very passionate about lights bulbs!

So we tested how different types of light tan the wood before varnishing. I made up two sample pieces of spruce and covered part of each piece with aluminum foil. The wood under the foil would remain untanned and would be a record of how the wood looked before any UV light.  The rest would be tanned under the different UV lights.


He took a 250 watt mercury bulb, modified it by removing an outer glass covering to increase the level of UVA and UVB. (Probably something left to an expert.)


The bulb used 110 volts in a basic set-up in the basement of his light shop. I ran the same test with my standard UV lights.




The result below was very interesting. The piece of wood on the left was in my UV light box. It did change somewhat but not a great deal. The wood on the right was under his light and is clearly tanned a light brown colour.  I’m now experimenting further with this new light.












I did end up replacing some of the older lights in my light box, which is where all this started.  I’ve recently learnt, concerning the UV tubes I have, that their light output reduces by half after 4000 hours of use.  So I’ll probably replace the tubes every 1 -2 years  to be sure they’re working at their best and say hi to the guys at the light shop.


One Response to “Tanning wood before varnishing”

  1. Tim K
    August 26th, 2012 @ 6:55 pm

    Very interesting idea, tanning wood with UV light. Can you tell us how many minutes the wood was exposed to this big mercury bulb on the darkest part of the wood?

    Oh, and question #10 on this page http://iuva.org/uv-faqs talks about this very idea. It is even suggested to first coat the wood with some Hydrogen Peroxide to enhance the effect. Have you ever tried that?

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    Guy Harrison Violin Maker
    792 Gladstone Avenue
    Ottawa, Ontario
    K1R 6X9
    Tel: 613 569 4803

    1997 Silver medal for viola in the Mittenwald International Violin Making Competition, Germany.

    2010 Bronze medal for violin in the Mittenwald International Violin Making Competition, Germany.

    2014 Workmanship award for violin in the Mittenwald International Violin Making Competition, Germany.

    2016 Silver Workmanship medal for cello in the VSA Violin Making Competition, USA.

    Member of the American Federation of Violin & Bow Makers and Violin Society of America.

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