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Cooking Colophony Down For Color, Low and Slow?


Berl Mendenhall
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I have cooked many different raw resins and colophony from different sources and I have found (and still) finding differences in color. I have only done one really long and slow cook using rhe Diamond G rosin. When the weather gets warmer I plan to try again.

Don what do you think caused the sludge in the DG rosin? I have never experienced that before in cooking any pine resins. The closest thing to sludge I got was when trying to make a sandarac oil varnish. It just turns to snot when adding the oil.

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Of all the people who have super-cooked colophony,  can someone report how it ages?  Does anyone have a 10 or 20 year old varnish sample to discuss?

 

I know that my first violins have Michelman varnish,  and it did not start to go bad until 30 or 40 years.  The first one is still sitting hear along with a couple other smamples.  One is not even my own.  These are the ones where the varnish has migrated into little islands,  discussed before.

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Don what do you think caused the sludge in the DG rosin? I have never experienced that before in cooking any pine resins.

 

Beats me  (it was actually the FF, not the DG rosin where I got sludge).  It wasn't the rosin, since I did successfully make some cooked FF rosin varnish from that shipment.  It was only when I tried to push it farther, trying to get more color by cooking hotter/longer, that I got the sludge.  Perhaps my cheap fryer had hotspots and created some odd results, but I don't really know.

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Of all the people who have super-cooked colophony,  can someone report how it ages?  Does anyone have a 10 or 20 year old varnish sample to discuss?

 

I know that my first violins have Michelman varnish,  and it did not start to go bad until 30 or 40 years.  The first one is still sitting hear along with a couple other smamples.  One is not even my own.  These are the ones where the varnish has migrated into little islands,  discussed before.

John,

My 10+ year samples are fine.

Joe

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  • 1 year later...

Another resurrected old thread, but a good one.

 

A bit of an update:  I finally got around to installing a thermocouple in the mini deep fryer I had been using, so I could operate it with a digital temperature controller rather than the original cheapo bimetal thermostat.  It is quite obvious now that when the thermostat kicked on, the 1000 W heater got to blazing high temperatures before the heat got back to the sensor.  I suspect that my previous fails were due to overheating and decomposition at the hotspots.

 

With the digital controller, the power is blipped on briefly every second, and the temperature (sensed very close to the heating element) only varies by 0.2C from the set value.  My guess is that previously there were swings of well over 100C.

 

Now with a well-controlled temperature on the bottom, I can tell that there is still quite a large temperature gradient through the resin.  With the cover in place, and just barely hot enough to be liquid, I found ~50C cooler at the top of the resin (only about 2 or 3 cm depth), and the top tended to get thick and taffy-like.  If I raised the temperature to get more flow, the differential decreased, but was still around 30C.  This would be a much bigger problem without a cover, and I think that to get a more uniform temperature I'll have to have a well-insulated cover.

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Interesting setup, how long do you intend to cook it?

 

I don't know time-wise.  As it cooks, it thickens, and then I'll raise the temperature to keep it fluid.  The stopping point will be when I reach a temperature that seems uncomfortably hot (I'm guessing somewhere in the 220 - 230 C range) and it begins to thicken.

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Stop pussy-footing around.  If you want a dark red/brown varnish, you need to get to at least 300 degree C.  I would add the rosin and oil at the same time.  Use a PID controller to control the temperature so you can turn your back on the process and not have it go up in flames.  Keep checking the color.

 

Yes, this is dangerous but it is the only way to know what is in the varnish.  Trust no one.

 

Mike D

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Hi Mike D- I use your way, combine oil, resin and a metal to make a resinate, run the temp up to something over 525-575oF, indicated by the formation of surface foam around 1/8-1/4 inch. When the surface foam starts to reduce or disappear, It signals the cook is done and stop the heat. A lot has happened chemically in that 25-30 minute cook.  fred

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 I strongly recommend a temperature controller. 

 

Me too.

 

 Also, I think the thermocouple should be solidly attached to the POT, and not in the resin or varnish.  The pot is a much better thermal mass, and can be controlled well.  Resins and varnish are terrible conductors, and you could get hotspots with sensing the varnish and heating the pot.  You can use IR or other thermometers to check the varnish itself, but controlling the pot is the safest bet.

 

BTW, I just bought a heavier deep fryer at a yard sale today for $5.  Not that I really need to make more varnish... but it seemed like too good of a deal to pass up.

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 You use a thermocouple at these temperatures--it is well beyond the range of a thermometer.  If you are going to use a PID temperature controller, the thermocouple provides the electrical signal needed for the controller.  I strongly recommend a temperature controller. 

 

 

Mike D

Sounds good, but how did you calibrate this?

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I've used an iron pot for cooking varnish for years. I'm not sure what effect it has on the color or darkening of the varnish. Although I'll probably be looking for a nice used stainless steel pot now, just to be sure. I've argued that I thought old varnish makers used cast iron pots to make their varnish in. I don't know what else they could have used, other than ceramic and I'm not really convinced of that. I can tell you that adding rust to the cook will make your varnish darker and a beautiful transparent red brown. Only problem is it doesn't stay that color. It gets darker, "MUCH" darker. I've got a fiddle in my shop now for a bridge that I made in the 1990's and it is way darker that when I made it. Very disappointing. It was a beautiful color when new. I've argued before I didn't think this happened to this degree, but I was wrong. God that's hard to say.

 

Iron darkens rosin and commercial makers of rosin go to great lengths to prevent iron contact (SS reactors, metal chelating agents) in order to make the rosin as light as possible.  Light colored rosin sells at a premium.   Heating rosin in a cast iron pot is very sensible if your goal is to make it dark.

 

I noticed in many previous threads discussion about using hot plates, various means of temperature control, and the problem of uniform heating.  In my profession, hot melt adhesive chemist, we would never melt resins on a hot plate or stove.  Ovens are much safer, easier to control, and heat uniformly.

 

Most importantly, remember that rosin vapors are harmful, and hot rosin is a fire hazard.

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Sounds good, but how did you calibrate this?

Hah, good question. So far, I don't know of any better way of calibrating my thermocouples than using a fluid-expansion thermometer. All the thermocouples I have used so far have changed over time, both when compared to a mechanical (fluid expansion) thermometer, and when using boiling water as a reference (and I realize that both the boiling and freezing points of water aren't etched in stone).

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I've been making some progress with the Hargrave recipe.

It's still not as dark as I would like but here are a few notes that might help. 

 

- Cook collophony at 180-190C in small steel container for however long it takes to thicken (5-7days).

-If cooked hotter, the collophony will not mix with oil. 
-Swirl occasionally to make sure top layer doesn’t form skin. 
-Heat linseed oil to 200C and slowly add and stir in collophony powder. 
-Cook until pilling stage approx 1-2 hours.
-Cool to below 100C and add mastic tears 5%.
-Stir and cook for no less than 1 hr. 
-dark vs light colophony doesn't seem to make much difference. Light colophony may yield more red?
 
The biggest problem I've been having is that the color fades pretty significantly in the uv chamber.
I've been using uvb reptile bulbs.  I just picked up some party black light bulbs to see if a more limited spectrum helps. 
Has anyone else experienced fading?
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The biggest problem I've been having is that the color fades pretty significantly in the uv chamber.

That's been my experience too. But if blasted with enough UV, long enough, it eventually seems to plateau, and become pretty resistant to further change.

 

It's definitely something one needs to be aware of though. One wouldn't want to dry the varnish for a day or two, and think that that's the final color. I'd give it something more like two weeks in a UV cabinet, before coming to conclusion about the color.

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