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Cooking Colophony Down For Color, Low and Slow?


Berl Mendenhall
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So can it be said that the color produced from cooking resin is purely the result of oxidization?  Some resins are more heat stable than others, yes?  Canada balsam, for instance, is said to be highly optically stable over time (with little color change) but has little thermal resistance.  Would such a resin be more reactive to cooking?  Has anyone cooked Canada balsam?  I imagine the optical clarity would be desirable, but I haven't played with it enough to know.

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the canadian balsam cooks up to a wonderful red....

after finding isolated thirty year old white pine pitch in an old roof ,drops of it, red as ruby ,I believe the oxidation is the colorant .heat and time...

Thanks Mike, now we're getting somewhere. Next question is where can a person get Canadian balsam?

Edit: Other than Canada. I just wanted to say it before someone else said it.

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Hi Davide- the only advantage to tube pigment is availability, the only place I found powdered umber was in a lumber yard where it is sold as a colorant for cement. Works fine, gives a clearer varnish since it is not ground as fine as tube pigment. Since the color  generated is the result of a chemical reaction between the compounds in umber and the acid fractions in rosin the degree of grinding has no bearing.

 

Hope you find what makes the deep reddish brown. It definitely seems to have something to do with the rosin. I add rosin and raw linseed oil 1:1 or 3:2, about 1/2 inch umber from the tube, heat it in a 4oz Gerber baby food jar for visibility (jar sitting in about 1/4 inch sand in a short can) to 550oF or so it maintains a head of foam around near 1/4 inch without falling. Try and hold the foam(10-15") until you see it wants to breaks up and clear areas form, indicating the chemical reaction is ending. Watch the small bubbles along the glass to start slowing, or check for a 8-!0 inch string, indicating it is ready to add turp.  Whole procedure is around 35 minutes. A ratio of 1:1 oil/resin gives you better leveling of the varnish.  fred

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Hi Davide- the only advantage to tube pigment is availability, the only place I found powdered umber was in a lumber yard where it is sold as a colorant for cement. Works fine, gives a clearer varnish since it is not ground as fine as tube pigment. Since the color  generated is the result of a chemical reaction between the compounds in umber and the acid fractions in rosin the degree of grinding has no bearing.

 

Hope you find what makes the deep reddish brown. It definitely seems to have something to do with the rosin. I add rosin and raw linseed oil 1:1 or 3:2, about 1/2 inch umber from the tube, heat it in a 4oz Gerber baby food jar for visibility (jar sitting in about 1/4 inch sand in a short can) to 550oF or so it maintains a head of foam around near 1/4 inch without falling. Try and hold the foam(10-15") until you see it wants to breaks up and clear areas form, indicating the chemical reaction is ending. Watch the small bubbles along the glass to start slowing, or check for a 8-!0 inch string, indicating it is ready to add turp.  Whole procedure is around 35 minutes. A ratio of 1:1 oil/resin gives you better leveling of the varnish.  fred

 

Thanks for your kind explanation, Fred.

 

The resin that I have cooked with umber was colophony pre-cooked with 2% lime, I only cooked the resin alone with the umber (without the oil) to see the color that I could get.

Has darkened considerably but the resulting 1:1 oil varnish made with this rosin reaches a sufficiently intense color in 8 layers and a very dark one in 10 layers (on rib samples)

Too thick for my taste, 6 layers would be good but still a bit 'washed-out color, maybe with a little red pigment added may work.

However, my ideal goal would be 4 layers at most and with intense color, but for this I think I need more color from the resin.

 

Your method to make the varnish is at the top of my list, I'll try as soon as possible, the brevity of  your cooking time amazes me, my rosin has several hours of cooking.

Do you think the reaction with the umber also has an effect on the color of the oil?

 

Davide

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Thanks Mike, now we're getting somewhere. Next question is where can a person get Canadian balsam?

Edit: Other than Canada. I just wanted to say it before someone else said it.

A friend who is trained in the 19th century atelier method of fine painting pointed me to KAMA pigments for the finest quality Canada balsam.  It's his preferred resin for use in oil mediums, due to it's clarity and color stability.  He's taken resin from the balsam fir, which is an easy tree to spot here in Maine or most anywhere north of the border.   I think it reaches all the way to Alaska? Christmas trees!

You can buy some here:

http://www.kamapigment.com/store/index.asp?lang=1&catpage=2420

Red when cooked?  I would love to see varnish samples!  I may have to venture out and collect some.

 

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Yeah, maybe your right...I guess I could give it another week just to see.

Edit:

It's back on the fire...so we'll see what happens in another week.

Day 13...the Diamond G rosin is getting darker so I'll continue cooking it for awhile longer. Maybe another week...I want to get it as dark as possible on it's own.

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I have a question...because I haven't cooked varnish before but I am going to soon...

Sorry for the low level of my question...

...

I know a tin can is popular instead of glass, but will that get the same result? Does the outside pot being steel matter? Is it usual to put sand in the pot or in the tin can (which contains glass, and the glass contains the varnish stuff)? My sense is that some are using 4 or more layers to get to 212¤...some are minimalist, using only the pot, sand, and glass.

The recipe I want to use is pretty simple, but these first steps are assumed. The only imperative is that the mix boils. But I wonder what the best setup is.

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I have been using a simple sand bath with glass , I think metal might have some extra effect .??? the glass seems good , I just made my biggest batch , about 8 oz , the best set up would be air heat to a thermometer set up , possibly with a sand bath to carry the glass. a water /sand /glass bath would get a 212 ...but I thing the varnish needs a higher heat , I let it come to a foam ,but no real smoke ,,, and then let it coast to cool  in the bath , also, stir with a wooden stick to insure a complete melt of the resins .test for stringing , I also use an over sized sand pot to catch any thing that might boil over ,,,just in case .

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Yes, thanks. Oversized pot is a good idea. I already scarred myself for life once this week (In my maker thread there's a horrible photo of what scalding water and coffee grounds did to my wrist, it hurts!) and I need to be careful with this!

The cook described by Adele Beardsmore in a trade secrets awhile back specified the use of only the steel or enameled saucepan. Everyone seems to uee the sand and tin can , and/or glass, and sometimes a second pot. This will get the cook up to temp more slowly I guess, & less likely to burn? Just curious what was done 500 years ago.

She wears a full haz mat suit for her cook, incidentally. Maybe a good idea for me if it weren't 110¤ out and if I had one. I am that accident-prone!

I ended up reading of an even easier varnish than hers also from that same British Museum document of old recipes she used, and I would like to try that one first. The moment the mix is boiling, it's done. Hey--I can handle that! Hahaha

But I really don't know what way to go with the set up aspects. The very easy recipe, as I mentioned, didn't specify.

Lots of the old recipes assume everyone knows the same set up method. That's frustrating.

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It looks like the colophony you guys are using is not dark enough?  After that long cooking it still looks lighter than my 45 min cook?

 

attachicon.gif2014-01-23 19.41.10.jpgattachicon.gif2014-01-23 19.42.45.jpgattachicon.gif2014-01-23 19.47.42.jpg

 

Cooking it hot gets it dark fast.  I have some copal that turned a golden brown about that dark.    Now if you boil linseed oil untill it turns a dark mahogany red and then use that to mix with the resin to make a varnish I bet it would look good ! 

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Cooking it hot gets it dark fast.  I have some copal that turned a golden brown about that dark.    Now if you boil linseed oil untill it turns a dark mahogany red and then use that to mix with the resin to make a varnish I bet it would look good ! 

 

Thanks Mike.

 

I cooked the colophony in low temperature 120 - 150 °C, total time of 45 min. I'm about to make new batch this week. I'll post some pictures later

 

 

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Any experiences on color stability on a fast, hot cook VS. a slow, low cook?  My limited experience, mainly with varnish from resin cooked slow and low, is that the color changes a lot in the first year or two after application.

In my experience, all heat-colored (pinish-based) resin, mixed with oil, lightens significantly upon drying. Once thoroughly dried or "plateaued", I think the color is pretty stable, but I can see how color changes could continue for a number of years if the coating isn't dried enough to begin with.

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Indeed.  It seems like that plateau that David mentioned is real though.   Once the color stabilizes, further UV treatment ceases to create a noticeable effect.  I had wondered about more aggressive treatments, such as ozone, on finished instruments.  I know there's debate as to it's efficacy in general.  Just wondering if it would have any effect on cured varnish.  Playing with fire, I know. 

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Is there any consensus on an average pH for varnish?  Are they generally neutral? Certainly these mineral grounds would have a pH effect.  However, Roger Hargrave's slaked plaster method is pH neutral, by nature of the slaking process. 

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