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Berl Mendenhall

Cooking Colophony Down For Color, Low and Slow?

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I'm going to make a batch of varnish later this spring. I'm going to wash the oil and cook the resin down first. My question is how long to cook the colophony and at what temperature. I know it's cooked at a very low temperature, I just not sure how low and how long. Thanks in advance.

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From my first effort I would make the following observations.

 

As Roger wrote in the bass thread, don't turn the heat off while the cook is on.  The resin will solidify and possibly burn when turned back on.

 

A very low boil, but with some movement of the liquid resin is good.  Too low a temperature that produces little if any fumes is going to make the cook take forever.

 

No less than 7 days without interruption.  The resin may look dark prior to that, but when diluted with linseed oil you'll lose a lot of intensity unless it's really really dark... black.

 

Better to run the cook when it's not cold outside.

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It's 2:00 in the morning and I'm up so I thought I'd respond to this. Thanks actonern.

That's a bit scary. Did you use a sand bath? I think that would help to keep a constant temp. Brian Lisus (quartet of peace video) used a plastic tub and set everything down in it and put a lid over it. That way he kept the weather out and kept it away from any buildings. I did see a cook being done at one of the violin making schools that was done inside the building, but it was cooked at a lot lower temp.

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From my first effort I would make the following observations.

 

As Roger wrote in the bass thread, don't turn the heat off while the cook is on.  The resin will solidify and possibly burn when turned back on.

 

.

No disrespect to Roger intended, but I've never found this to be any problem whatsoever. I regularly cook rosin in several 8 hour sessions to accumulate enough cooking time, and never get any burning.

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From personal experience, a sandbath prevents the local buildup of temp in the colophony and allows heat-stop processing over weeks. A good secondhand lab hotplate prevents initial temp spikes while getting to <200 C.

 

I was about to start another long colophony bake, but this was aborted because the pine pollen has made everything yellow.

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Funny, that mention of burning by Roger stuck in my mind. I think (repeat think) that Roger's burning on the pot bottom when reheating was due to too high a burner temperature. I imagine that you should slowly build up the temperature to allow the entire batch to melt. Of course, that may be easier said than done for some setups.

 

What I do remember is that so much of the colophony boils off. I wonder whether I was cooking at too high a temperature. The objective is to oxidize the colophony not evaporate it. I think 80% went into the air. 

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From my limited varnish making, I've found some things leave less than others;  for example, I cooked up some larch turp  and some Canadian Balsam at the same time, and there was not nearly as much left of the latter.

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I usually cook varnish at temperatures around 280-300 degrees Celsius. For 3-4 hours I have done. I make small batches, it goes faster. 

 

Resin to first cook itself. Is there a big weight loss. 

 

For example, Venetian turpentine 300 ml cooked 280 degrees, and I'm only 40 gr resin 

 

Interesting for me. My varnish reacts to alcohol after polymerization. Can rubbing alcohol.

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I attempted to answer this and lost it after writing a whole page. A lot of this and more is on the ‘Making a double bass’ blog, but  here is some of it again. I bought myself a small plastic and aluminium green house from a garden centre. This protects the stove and pot from inclement weather. It cost about 25 euros. It is only about three feet high so I set it up on bricks, but make sure that it is very stable. You don’t want anything falling over. It needs to be high enough for the stove, the stainless steel asparagus cooking pot and some clearance. Mine opens at the top to let the fumes out. At the beginning there are a lot of stinky sulphurous yellow fumes. These will not please the neighbours if you live in a town. I suggest you find a friendly lab or move to the country for a while. Your electricity bill will be high, especially if like me you occasionally cook in the winter. However, cooking outside in summer is an added fire risk. These things can go exothermic and if you are cooking for several days and nights, you cannot be there all the time. Also certain types of clothing can fill with fumes and ignite, so have a good extinguisher close, but not too close. Make sure that it is one that can tackle an oil type fire.  

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No disrespect to Roger intended, but I've never found this to be any problem whatsoever. I regularly cook rosin in several 8 hour sessions to accumulate enough cooking time, and never get any burning.

 

No disrespect to you either John, but if you want to get the effect that you can see on my bass blog you need to cook for a very long time; as Actonern says, until it appears to be black. If you do this it will solidify instantly when it cools and it is very likely to burn when you try to re-melt it. I also use a sand bath. As  well as helping to prevent fire (if the stuff boils over) it also helps to disperse the heat around the pot rather than having it just coming from the bottom. And yes Michael lots of it boils off and whether it is oxidizing or whatever it is doing, it does the trick for me.  I would say that your 80% loss is about right. 

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From my limited varnish making, I've found some things leave less than others;  for example, I cooked up some larch turp  and some Canadian Balsam at the same time, and there was not nearly as much left of the latter.

Also right, and there are even differences between colophonies. This is the reason why recipes and temperature charts don't work very well. You just have to play it by ear each time. As I also said on the bass blog, especially at the beginning, don't be tempted to cook big batches because some will always go wrong and bigger batches mean bigger waste.

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Oxidize... exothermic...color...

This sounds a lot like cooking oxidized turpentine.

 

Does anyone know the chemistry of what's going on here, and if you're ending up with some amount of terpene resin when you slow-cook rosin?

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Oxidize... exothermic...color...

This sounds a lot like cooking oxidized turpentine.

 

Does anyone know the chemistry of what's going on here, and if you're ending up with some amount of terpene resin when you slow-cook rosin?

I bet some of this was covered by Fulton. I don't think I still have his books.

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Oxidize... exothermic...color...

This sounds a lot like cooking oxidized turpentine.

 

Does anyone know the chemistry of what's going on here, and if you're ending up with some amount of terpene resin when you slow-cook rosin?

 

Don, I love reading your posts, but sometimes you scientific bods want an explanation for everything. Can't you just be satisfied when it works?

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Don, I love reading your posts, but sometimes you scientific bods want an explanation for everything. Can't you just be satisfied when it works?

 

I have a bit of a hidden agenda here...

If the bother of cooking down rosin for days is only to end up with mostly a terpene resin, then:

A - I don't need to do that, as I have a big stock of terpene resin on the shelf, and could just use that

B - I had extreme difficulty trying to make a varnish out of terpene resin... ended up as useless glop... so I might just give this idea a pass.

 

So, if it's something OTHER than terpene resin that gives the cooked rosin the color,  then I'm much more inclined to want to try it.

 

And no, I'm never satisfied with just doing stuff that works.  It's just a character flaw I have to live with.

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Roger,

 

This you have likely answered before but anyway;

 

What is the most reason for the long cooking, to get the colour or other properties in the varnish?

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Roger,

 

This you have likely answered before but anyway;

 

What is the most reason for the long cooking, to get the colour or other properties in the varnish?

 

Just colour! I mainly use it as a pigment, which defeats Dons arguments, because Dons stuff will never be dark enough if it remains as he discribes it. More details are on the 'Making a double bass blog'. We are now very close to finishing the editing, after which I will put the link on that blog. I think all the work has been worth it. Although it is much shorter, there is a lot of new material and everything is now in the correct order. 

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Don, I bet there are any number of things that you use and do, without ever understanding how they work. As my mother used to say, "You don't know everything!" Of course in my case she was wrong, but I never held it against her.  

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Hi all

 

How to manage the low temperature, only watching the resin pot?

 

I read when we drop a feather and this burn immediately the varnish is very hot.

I am thinking to use a sand bath pot for low heating.

What symptom can we see when it is at low temperature if we do not use a thermometer to measure?

 

 

Thanks

Tango

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Don, I bet there are any number of things that you use and do, without ever understanding how they work. As my mother used to say, "You don't know everything!" Of course in my case she was wrong, but I never held it against her.  

 

Computer.

Internet.

Sewage treatment facilities.

 

Yes, there are limits to my interest in how things work.  Next time the MN site starts behaving badly, I'm glad you will be able to sort it all out.

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Tango, Don suggested in another thread a Thermocouple, I believe something like this one, coupled with a relay and a temperature sensor may be the way to go, it is what I will be setting up as soon as spring hits the NE Atlantic..need to do some research on which thermocouple to buy still....it should be a 40$ investment, well worth the safety.....all stuff you can find easily in Buenos Aires..

 

and a relay (just as an example)

 

Thanks Don. :)

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Tango, Don suggested in another thread a Thermocouple, I believe something like this one, coupled with a relay and a temperature sensor may be the way to go, it is what I will be setting up as soon as spring hits the NE Atlantic..need to do some research on which thermocouple to buy still....it should be a 40$ investment, well worth the safety.....all stuff you can find easily in Buenos Aires..

 

and a relay (just as an example)

 

Thanks Don. :)

 

That gadget looks just super. The feather trick is mentioned by several renaissance writers, but it is a bit too hit and miss. I just had access to a high temperature thermometer. When I was not there I simply turned everything down. The important thing is that it is not allowed to solidify (set hard). It will get like thick tar, but it should not set, because that is when it is likely to burn when the heat is turned back on.  

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I have to ask,  instead of cooking long and slow, what's wrong with hot and fast?   And why is a little bit of burn undesireable? 

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