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Side post : ancient wood finishing recipes from the French Masters (Boulle & Watin)

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Blog entry by Sodabowski posted 11-27-2017 10:05 AM 3923 reads 1 time favorited 6 comments Add to Favorites Watch

Hi Jocks,

in a blog post from my buddy Shipwright, where he experiments with finishes and their relationship with colorfastness of the wood, I talked a bit about sandarac. LJ member Longcase contacted me by direct message to inquire about that stuff. Long story short, sandarac is the resin produced by a tree, and has been used for centuries for wood finishes, along with the other classics that are shellac, elemi, mastic, and the many essential oils like aspic.

The guys at the C2RMF, where I pursued my Physics Master Degree internship, have experimented with these ancient recipes, and given the freaking technical means that they have (anyone heard of the AGLAE particle accelerator?), they devised what to date seems to be the very best color-protecting wood finish. Here’s the original article they published (in French, sorry folks, don’t worry I’ll give you the translation of the interesting part below) : http://c2rmf.fr/sites/c2rmf.fr/files/etudevernisdernier.pdf

Fast forward across the document to what you’re really looking for, this is the best performing recipe they found:

First layer (applied with a badger brush):

100 mL Butanone
15.5 g Sandarac resin
6.2 g Chios mastic (that’s the expensive stuff, yeah)
3.1 g elemi gum
3.1 g aspic (lavender) oil

Second layer (applied like a french polish):

90 mL Isopropanol
10 mL Butanone
15.5 g Sandarac resin
6.2 g Chios mastic
3.1 g elemi gum
3.1 g aspic (lavender) oil

Warning :

- the curators from the Louvre found out that this is way too shiny for Ebony, and on that one they use petroleum wax instead.

- from my own experiments with them, the wood stained green by Chlorociboria (you know, my pet fungus), really dislikes the Sandarac mixture and turns yellow (ie this recipe raises the pH of the wood above neutrality).
If you’re not working with naturally-stained green wood from that fungus, no worries, it’s really the only case of bad behaviour we’ve seen so far. For all the classic woods the results are excellent even with very strong exposure to UV light. I’m working on an alternative recipe formulated for Chlorociboria stained woods.

Almost all these ingredients can be purchased online, even on eBay. Beware of the Chios mastic though, be prepared to pay a premium for that one (around $300/kg). And no, you can’t set one of the ingredients aside and hope for the same results. This formulation is the result of months of professional testing by the top three professionnals we have here in France.

Cheers

Thomas

-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...



6 comments so far

View Longcase's profile

Longcase

97 posts in 1567 days


#1 posted 11-27-2017 04:23 PM

Thomas, Thanks for this, very interesting .
Couple of questions to start with
Should the first coat be sanded back ?
How many second coats are recommended overall protection ?
Keith

View Sodabowski's profile

Sodabowski

2374 posts in 2953 days


#2 posted 11-27-2017 05:33 PM

Oh, good one, I don’t know. Since we were only trying to test the colourfastness I didn’t sand between coats. I think you could, but since the Roubo mixtures are quite on the thick side and they dry very fast, I’m not even sure the grain would have any time to rise. Two coats should be plenty. Once fully cured this stuff is very strong yet not brittle (thanks to the oils)

-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...

View shipwright's profile

shipwright

8069 posts in 2918 days


#3 posted 11-27-2017 11:51 PM

To clarify Thomas, is this a new formula that these scientists have arrived at or is it the result of analysis of an old finish? If it is in fact an authentic “ancient recipe” then we are still looking because the ancient marquetry is not holding up colour-wise.
My experiment is about testing the UV filters found in modern varnish and the atmosphere sealing qualities of epoxy.

.... all very interesting anyway!

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View Sodabowski's profile

Sodabowski

2374 posts in 2953 days


#4 posted 11-28-2017 09:52 AM

No Paul, this is the adapted recipe, a lot of UV exposure and precise color measurement was done during this lengthy seris of experiments by the scientists. This won’t play the tricks that Boulle and the others had.

-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...

View Woodknack's profile

Woodknack

12338 posts in 2500 days


#5 posted 12-15-2017 07:22 AM

Even though I’ll never try this finish, this discussion is why I love the internet.

-- Rick M, http://thewoodknack.blogspot.com/

View Sodabowski's profile

Sodabowski

2374 posts in 2953 days


#6 posted 12-15-2017 08:44 AM

:)

-- Thomas - Pondering the inclusion of woodworking into physics and chemistry classes...

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