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wm_crash

Copal oil varnish - fail

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Hi,

 

I decided to try my hand at oil varnish cooking today. Short of starting a big fire, the results were mostly a learning lesson. I'm still trying to figure out what I'm learning, so that brings me here.

 

I started with:

200mL cold pressed linseed oil

180g myrrh (later to be replaced with copal)

2 brand new Emeril 1.5qt stainless pans from Bed Bath & Beyond

 

I fired up the oil and cooked it until it got darker, and then I turned it off. The myrrh just would not melt. It caught fire twice, but didn't melt. At that point, the reciepe changed. I melted 180g manila copal (from Kremer Pigments). I added some ash water and a bit of sinter lime water (Kremer again).

 

Once the copal melted, I cooked it for 30 minutes at 230C or so, then I added the oil. The oil was noticeably cooler because it had cooked while I was plying with the myrrth. The copal sorta hardened, but then everything mixed nicely together. I cooked that for about 15 minutes, and made a string test. I got a nice 2" string, but I thought I'd let it cook a little bit more. Apparently, that messed it all up. The whole thing turned into a glob of dark jello.

 

Any pointers towards what I am doing wrong would be appreciated.

 

cheers,

wm_crash, the friendly hooligan

 

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Looks like you`ve burnt it!!

Did you know only 44 % of Mryrrh is actually resin,it contains balsams, water and allsorts of stuff.

Regarding the copal, copals vary considerably and are not the best resin to use if you don`t have much experience of varnish cooking.Copal varnish is pretty difficult to make successfully.

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Sorry to say but it looks even worse than my first attempt! The oil caught fire and I overcooked the resin. I ended up with a varnish of sorts. A bit murky looking, odd greenish tint. Dried ferociously fast, even without a drier.

You'll have to control the heat and don't ignore the safety aspect. This can be dangerous stuff and the fumes can hardly be good for the old bellows. I gave up and switched to spirit. 

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Using a sand bath will help spread and modulate the heat,and provide a safety buffer in case of spillage.an air bath would be best but might be harder to tool up for. A good cheap source of cooking containers is food bottles like ball Jars or Mason Glass, buried in sand in a larger container to take the heat. using silicon padded tongs it's easy to gently lift the glass from the sand after cooking. better to under cook than over cook.

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well, at least you weren't skydiving.....my guess, too much heat with bad distribution.

 

edit: I would add, that after one goes through all this, spends the money on pans and materials, factors in the labor time, one starts to see the value and appreciate the expertise of Joe Robson's varnish.

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Well, I tried again this morning. This time I used the covered grill and container on the upper shelf of the grill for more uniform heat, and kept the heat lower than before. Had a heck of a time getting the copal to melt. In the end, it turned foamy and sorta kinda melted, but not fully. It was more of a foam still with quite a few solid pieces. I added the oil anyways and mixed and cooked some more. It was slowly going towards the same gummy mess as before, so I stopped right there.

 

Alright, time to step back and reevaluate. Thanks to all for the help.

 

cheers,

wm_crash, the friendly hooligan

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Hi Wm-Crash-. David Burgess is probably right in that you overcooked the linseed oil to gelation. I make a fossil Congo copal varnish  and don't know the process for the Manilas. I've attached part of a text on Manilas that might help.

 

I encourage you to experiment, keeping in mind oil can only be cooked for ca 20-30 minutes over 600oF before it becomes insoluble gel. A good start is bring your resin to a slight foam on the surface. Hold a constant temp and when the foam starts to break up add oil Use 1:1 resin oil and cook small batches. You should cook to a 8-10 inch string, just below the stuff gelling. This is roughly my process with Congo Copal, but this is a stubborn resin and you have to make a set up to keep hot walls otherwise it creeps away from the bottom and what is there just burns. You'll have a very nice varnish when you get it right, and adding a little rosin and umber at the start you'll bet a color similar to the old inst's.

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cut way back on the amount you make first time, as  you may want to repeat the process a few times before you get it right.  I usually do small batches that fit in an empty tuna can, and can do it many times before the investment becomes a point of sensitivity.   AND, I still get enough to do a test run with several coats on left over rib wood scraps.

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Many years ago I experimented with cooking varnishes and I cooked nice copal varnish using ready made picture varnish (it was UMTON Magistral varnish if I remember correctly, likely no more available). That was basicly congo copal dissolved in turpentine with some dammar added. I cooked it just till all solvent evaporated and then boiled it into linseed oil in roughly 50-50 ratio and added a mastic tear or two (I started with 100cc of original product and ended with little less of my oil varnish). The varnish brushed and levelled very welll on samples leaving very nice subtle texture and it was soft feeling while very durable at the same time, nice pale amber color, too. I still have a block of maple I use for trimming purfling and binding on my bench that I varnished with the varnish almost 20 years ago and it is still quite lustrous where it didn't wear away. If I wanted to cook copal varnish I'd probably look for some picture varnishes as source of copal to save me from the messy fusing and cooking of raw resin.

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Manila copal is not considered an oil soluble (when cooked) resin.

Joe

 

I'm sure you have more experience with many more resins than I do, Joe, but I've cooked Manila Copal & Mastic into a very usable oil varnish in the past. I believe some old recipes for Manila Copal in oil exist here and there... It has a lower melting point than other Copals as I recall... 

 

I use it mainly as a component for spirt "fill varnish", however.

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I'm sure you have more experience with many more resins than I do, Joe, but I've cooked Manila Copal & Mastic into a very usable oil varnish in the past. I believe some old recipes for Manila Copal in oil exist here and there... It has a lower melting point than other Copals as I recall... 

 

I use it mainly as a component for spirt "fill varnish", however.

Jeffery,

As there are many different resins that are labeled as "Manila copal" I think you just got lucky!

Joe

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Jeffery,

As there are many different resins that are labeled as "Manila copal" I think you just got lucky!

Joe

 

Maybe!  :-)  Last batch was Kremer (8 years ago).  Earlier batch was a different supplier.  Both behaved the similarly... Both sets also went into alcohol.  

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I have some copal that I think is manila.  It dissolves easily in alcohol.   I tried making oil varnish with it and it turned into chocolate colored concrete.    There used to be a website , lakemont strings,  that had a good description with pictures of making a copal oil varnish.   They made it look easy. 

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Hello

To me it happened when I was doing the varnish sandarac. It behaves like other fossil resins

Here at the forum was the advice. First melted resin to take place pyrogeneze. about 300 C for about 20 minutes. Further reduce the temperature to 250C need and then you can take the oil. Give the same hot oil in small pieces and stir. Oil is involved and can reduce the temperature for the addition of other resins.

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With the proper set up it is pretty routine to make a Fossil Copal varnish. Copal resin also has resins that are not very old and are alcohol soluble, so it is necessary to select your grade. Copal resins needing to be depolymerized (bonds ruptured) by heating are classed as fossil. I think this also exists in grades of Manila. 

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OK, I am willing to try the copal I have a few more times in about a week. I am getting a thermocouple to have a better handle on temperature. I gather that the resin needs to be heated way high to break down before expecting it to run. Does this need oxygen, or can it be done in a covered container?

 

cheers,

wm_crash, the friendly hooligan

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Hello

I made an example

I invented the recipe

 

30 g sandarac .......... 90 g linseed oil (1: 3) ---- copal will

  similarly

30 grams of resin from Venetian turpentine ....... 30 g linseed oil (1: 1)

30 g mastic ------------------------------------ 30 g linseed oil (1: 1) .....................   150g oil

 

........  90 g resins                                                            total ratio 1:1,66  

1 / C 300 sandarac first foaming and raging --- it must wait until it calms down

2 / slowly are adding hot oil was ja 250 C

 

3 / lower temperatures, and you add another resin

 

 

can then cook on low heat to high heaven as you like

 

I will continue to about 150 C for many hours

I'm happy I managed to

 

I think copal resin that will be very similar

 

I give the photos are not very good, but just

 


Wife saw what I was doing on our grill.

She was furious as he Sandarac

... And he wants a new grill

.... Okay let her spend too, especially that I have a new varnish

 


Fear and try

I've learned this thanks to the forum maestronet and will also help


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Thanks Mumbleypeg, that is where I learned the process.

 

Violinoalto, I'm pretty sure you can't cook fossil copal resin and oil at the same time. It will gel before the resin becomes oil soluble. It takes around an hour to make the varnish. I make enough to varnish 2/3 inst's at a time.  The key to cracking copal, a thermometer isn't necessary, is to heat it to around a  surface foam  that is  roughly equal to the height of the contents. That is a temp around 620-50oF. This takes around 25", the foam sort of rapidly disappears and there is shiny black quiet liquid that looks like it is shimmering ( the resin is boiling quietly) indicating it is cracked. Get the oil hot and add to the slightly cooled resin. Cook to string, cool and add  turp to a level drip on glass.

 

That's the basics to make the varnish. I haven't made it in years. Right now I am on Doxycycline for a bad tick bite, miserable from the antibiotic and the bite. Feel like you've beaten up and have a bad cold, so it will be a while before I feel like doing anything.

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