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Cooking Colophony Down For Color, Low and Slow?


Berl Mendenhall
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The wrong pH can also fade color over time.  Balancing the ground and the finish to a neutral pH is wise, but kind of hard to measure.

Hard to measure, indeed. pH actually only applies to aqueous systems, which most varnishes are not. Acidity/alkalinity can apply to many systems but in a different manner than pH, which is one of the most misunderstood aspects of chemistry.

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Right, so pH only measures ionic activity in a solution with water.  Abietic acid is not soluble in water.  Organic acids are considered to have acidic properties, meaning they tend to give away their protons. So in discussing varnish, we are in a murky area involving acids that are only soluble by solvents.  The pH measurement process is a product of the Arrhenius Acid definition, which specifies acids by their solubility in water.  There are two independent definitions that expand the nature of an acid.  Brønsted-Lowry acids are substances which give up a proton to a base.  Furthermore, Lewis acids react to a base by way of electron pair transfer.  The last definition acts as an oxidizer.  
Are the organic acids in tree resins Brønsted-Lowry acids, Lewis acids, or both?  They are not the Arrhenius acids which are measured by pH.  
I am spouting off readings.  My capacity for chemistry is limited beyond this.  

From a practical standpoint, non-Arrhenius acids can be altered by the presence of a base, and therefore react in a similar manner to our familiar water-soluble acids.  So measurement is tricky, but intuition guides one to stabilize the resin acids by addition of lime, or a similar base.  Are there other systems of measurement than pH?

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Right, so pH only measures ionic activity in a solution with water.  Abietic acid is not soluble in water.  Organic acids are considered to have acidic properties, meaning they tend to give away their protons. So in discussing varnish, we are in a murky area involving acids that are only soluble by solvents.  The pH measurement process is a product of the Arrhenius Acid definition, which specifies acids by their solubility in water.  There are two independent definitions that expand the nature of an acid.  Brønsted-Lowry acids are substances which give up a proton to a base.  Furthermore, Lewis acids react to a base by way of electron pair transfer.  The last definition acts as an oxidizer.  

Are the organic acids in tree resins Brønsted-Lowry acids, Lewis acids, or both?  They are not the Arrhenius acids which are measured by pH.  

I am spouting off readings.  My capacity for chemistry is limited beyond this.  

From a practical standpoint, non-Arrhenius acids can be altered by the presence of a base, and therefore react in a similar manner to our familiar water-soluble acids.  So measurement is tricky, but intuition guides one to stabilize the resin acids by addition of lime, or a similar base.  Are there other systems of measurement than pH?

Holy Moly...whadda he say?????????? :wacko::blink::huh:

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Holy Moly...whadda he say?????????? :wacko::blink::huh:

I don't talk like that in person!  Late night research get's the best (worst) of me.   :) 

Basically, no point talking about pH!  It's the wrong system of measurement for the acids we are dealing with.  However, the concept is similar enough, so use your good fiddle-making instincts and neutralize your acids when cooking, or not, because none of the acids we are dealing with are particularly strong.   Right?  Maybe?   :blink:   Ok, goodnight!

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As I've mentioned before, "acid number" is commonly used as a measure of acidity for such things as rosin. Commonly done by titration with potassium hydroxide dissolved in alcohol. ("Base number" is much less used.) Rosin usually has an acid number in the range of 160 + or -. One of my derivatized rosins has an acid no. of 34 to 40 and the other 0 to 14. A partially polymerized version (not neutralized) is specd at 140 to 160.

 

In practice, acidity of the varnish probably doesn't matter much, since we're talking a very weak acid. An alkaline ground under the varnish might be more serious.

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Not if you use maleic or rosin modified phenolics obtained by hydrogenation, polymerization and disproportionation of rosin acids, you loose sleep just thinking of it...

I wouldn't think of it.

 

All I think about when I sleep is being out in the ocean gently rocking,,

on your boat with a fiddle a guitar a piano, a set of drums a bass and some recording gear.

and you.

 

and maybe the kitchen sink.

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Not so.

I followed the recipe on Youtube from Geoff and when finished the rosin looked just like a piece of caramel. There was zero transparency. How do you incorporate lime so that it is still transparent?

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Maybe I'm using the wrong kind of lime? I followed this method and it seemed to incorporate OK but looks exactly like caramel. Look at his resin in the pot...

 

I started with some Diamond G colophony which is very clear and transparent. It quickly lost all transparency and I got the same looking stuff that is in Geoff's pot. I made a small batch and discarded it. I should have actually made a batch of varnish with it. Maybe it does clear up after the oil is added and cooked. So I could be wrong about the clarity...I used Kremers slaked lime.

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To get back to the original topic...My low and slow cook has reached day 19. The color is continueing to darken into a very nice dark red brown. Of course in a thin film it will probably still not be red but a nice warm golden brown. The brown is different than the brown color I get when I cook it fast and hot. This seems much more reddish. And my camera isn't picking up the red color as it really looks. I like Evan's idea of using the crock pot. It keeps the resin liquefied but not too hot. I'm leaving the cover slightly cracked and the temp holds a steady 275-285F. I check it several times a day and give it a good stir. Thanks for the tip Evan. This is proving to be interesting. I'm anxious to make some varnish with it but will continue to cook it awhile longer.

Maybe another week or so...

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How do you incorporate lime so that it is still transparent?

 

I make a thick paste of slaked lime with a little water and add it to the rosin and stir in.

 

There is foaming, frothing and gnashing of teeth (mostly steam). In the end, there are some 'precipitates' at the bottom of the pan which I take to be calcium rosinate or unused lime.  I decant the cooked rosin into a new vessel before adding the oil.

 

I have checked the varnish on glass and it is completely transparent. 

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To get back to the original topic...My low and slow cook has reached day 19. The color is continueing to darken into a very nice dark red brown. Of course in a thin film it will probably still not be red but a nice warm golden brown. The brown is different than the brown color I get when I cook it fast and hot. This seems much more reddish. And my camera isn't picking up the red color as it really looks. I like Evan's idea of using the crock pot. It keeps the resin liquefied but not too hot. I'm leaving the cover slightly cracked and the temp holds a steady 275-285F. I check it several times a day and give it a good stir. Thanks for the tip Evan. This is proving to be interesting. I'm anxious to make some varnish with it but will continue to cook it awhile longer.

Maybe another week or so...

Are you taking samples each day to determine that the color is indeed darkening and getting redder? If so, I would love to see them because I wonder if this stuff reaches a plateau and continued heating produces little improvement.

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Maybe I'm using the wrong kind of lime?

 

One thing to consider is not the lime itself, but the watery-ness of the mixture.

 

If the precipitates of calcium rosinate, for example, are very fine, then the rosin will appear like muddy caramel, rather than forming large accretions at the bottom of the pan.

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Are you taking samples each day to determine that the color is indeed darkening and getting redder? If so, I would love to see them because I wonder if this stuff reaches a plateau and continued heating produces little improvement.

Mike, I look at it daily and it is a slow process. I can tell that it is getting redder just from the photos I been taking. I would not say that it is a ruby red but more on the brown side. Definitely more of a red tinge from a week ago. And definitely more dark too. I'm talking about the yellow color in a thin coat. It seems more golden brown than yellow from a week ago.

Here are some close up's as Janito recommended...As you can see it is more on the brown side. But maybe in another week more red will develop. I'm very curious as to what it will look like after 30 days of cooking. Patience is key here. And I may be expecting too much from this particular rosin but I'm going to push it to the limit. I'have a hunch that there are better resins to cook to get a nicer red than the Diamond G colophony.

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