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Cooking Colophony Down For Color, Low and Slow?


Berl Mendenhall
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My goal in reducing the acidity of the rosin was to make the final varnish more stable over time, rather than changing in nature and going quickly downhill, as it seemed to do when the rosin was untreated.

 

There's also quite a bit in older varnish literature about commercial rosin varnishes degrading quickly, and hence only being suitable for cheap work. I don't recall if these references specified that this was with limed or un-limed rosin.

 

Again, my presumption is that the linseed oil component isn't happy in the acidic environment, since either component seems to be pretty stable before they are combined. But that's just a guess.

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I'm going to cook a batch today with limed rosin and see how transparent it is. This is the last of my oil so I hope it doesn't flop.

Finished liming the rosin. the clear rosin is now opaque same as last time.

I heated the oil to same temp as the rosin and combined...and crossed fingers.

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I'm going to cook a batch today with limed rosin and see how transparent it is. This is the last of my oil so I hope it doesn't flop.

Finished liming the rosin. the clear rosin is now opaque same as last time.

I heated the oil to same temp as the rosin and combined...and crossed fingers.

If there is excess lime in the rosin, be patient and allow several weeks - even months - for the excess to precipitate out.

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This is a quote- " These defects can be partly eliminated by neutralizing the acidity of the rosin with a base such as lime (calcium hydrate) or zinc oxide, or by combining with glycerol, thus forming "ester gum"

"When lime is employed to neutralize the rosin, the resulting product is knows as "limed hardened rosin", and the method is generally known as "liming". This is usually effected by first melting the rosin, then heating to 450oF(322oC), and slowly sifting into it finely powdered lime while constantly stirring; then raising the temperature to 525oF (274.4oC) and holding it at this temperature until the reaction is completed. The temperature of the batch is then permitted  to drop to approximately 350oF (177oC)  and it is thinned with mineral spirits. This varnish is known as "Gloss Oil"."

 

No more than 6% lime is usually  used, it should be free of moisture and not contain magnesium which will create insoluble soaps.

I wonder if liming is desireable if you are going to long cook it, for the process is some form of oxidation I guess, for the acidity goes down, the melting point goes up as it would with time and exposure to air. Be nice if someone does it both ways with the same materials. fred

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If there is excess lime in the rosin, be patient and allow several weeks - even months - for the excess to precipitate out.

Hello J.

Does your varnish get crystal clear after months of sitting. Right now while it's cooking it looks like a bowl of mud. All the varnishes I have ever cooked remained transparent. However as I'm testing for a firm pill the few drops on a piece of wood when spread out look transparent enough. I don't know how multiple coats will look. So it may take months for the lime to precipitate out and get clear again?

I guess if it's more stable than some loss of transparency is worth it.

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Hi Fred,

 

That's interesting. It directly contradicts the "lime + water" low-temperature method which has been mention in this thread.

That's what I used. I tried making a thick paste with water but I felt there where too many particles. Thinner has very little particles. Here is a photo of what it looks like as it is cooking. Looks very muddy to me but a drop on wood doesn't look too bad.

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Hello J.

Does your varnish get crystal clear after months of sitting. Right now while it's cooking it looks like a bowl of mud. All the varnishes I have ever cooked remained transparent. However as I'm testing for a firm pill the few drops on a piece of wood when spread out look transparent enough. I don't know how multiple coats will look. So it may take months for the lime to precipitate out and get clear again?

I guess if it's more stable than some loss of transparency is worth it.

Hi emv,

 

Yes, it takes some serious time for the lime to precipicate out. It eventually settles in a very distinct layer at the bottom of the container, and the varnish is absolutely crystal-clear.

 

As I've mentioned in a previous post, I wish I knew EXACTLY what was going on. I used 5% of lime, added to slow-cooked Kremer's colophony, done the "wet" way at 135ºC. Obviously some of the lime didn't react with the colophony, but the resultant varnish is noticably "harder" that just the straight colophony/oil version.

 

I imagine it would help if I knew precisely what the acid number of Kremer's colophony is, and knew precisely what the properties of the lime I used are. On the other hand, I'd be happy if the worst part of a lime OD is that one simply has to wait for the excess to precipitate out.

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That's what I used. I tried making a thick paste with water but I felt there where too many particles. Thinner has very little particles. Here is a photo of what it looks like as it is cooking. Looks very muddy to me but a drop on wood doesn't look too bad.

That looks quite radical. The method I used was to add a little lime, with a few drops of water, and gradually incorporate more lime over a period of 90 minutes.

 

I've lost the link to the following attachment, so I'm uploading the document - have you seen this?

 

Lime Rosin patent.pdf

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After all this, I do believe that for my purposes the Kishony/Hill recipe works best as far as the acid-neutralizing part goes. Water filtered through vine ashes with some lime added. I don't think a "complete" (if it is possible) neutralization of acid is necessary, just a lowering. One can use the resin prepared in that way with oil only (not adding gum spirits). One can slow-cook the resin (colophony, Burgundy resin or Strassbourg turpentine - or - a mix) for color before liming.

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Hi emv,

 

Yes, it takes some serious time for the lime to precipicate out. It eventually settles in a very distinct layer at the bottom of the container, and the varnish is absolutely crystal-clear.

 

As I've mentioned in a previous post, I wish I knew EXACTLY what was going on. I used 5% of lime, added to slow-cooked Kremer's colophony, done the "wet" way at 135ºC. Obviously some of the lime didn't react with the colophony, but the resultant varnish is noticably "harder" that just the straight colophony/oil version.

 

I imagine it would help if I knew precisely what the acid number of Kremer's colophony is, and knew precisely what the properties of the lime I used are. On the other hand, I'd be happy if the worst part of a lime OD is that one simply has to wait for the excess to precipitate out.

Kremer describes the acid number range of their common colophony as 162 - 178 mg KOH/g.  I am learning how this categorization works.  To quote WIkipedia:

In chemistry, acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance.

Soda lime contains ~1% potassium hydroxide.  Other components of lime include sodium and calcium hydroxides.  I am not sure how these chemicals interact with the acids in the resins, but hopefully these number help lend some sense to the process.

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Hi Jacob- I missed the post where water is added with the lime.  I imagine in the patent on lime there is a reason for the water, but the one I posted making Gloss Oil does says be sure there is no  moisture. If I were going to neutralize rosin I would use zinc oxide and not lime

 since it would help in preventing after tack in the varnish after it has been applied to something in a very humid area. fred

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Kremer describes the acid number range of their common colophony as 162 - 178 mg KOH/g.  I am learning how this categorization works.  To quote WIkipedia:

In chemistry, acid value (or "neutralization number" or "acid number" or "acidity") is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance.

Soda lime contains ~1% potassium hydroxide.  Other components of lime include sodium and calcium hydroxides.  I am not sure how these chemicals interact with the acids in the resins, but hopefully these number help lend some sense to the process.

For comparative value, most sources put the "acid number" of linseed oil between 4 and 6. Alkali-refined oils can be pretty close to zero.

 

I searched long and hard for the "acid number" of more familiar materials, like vinegar and lemon juice, to try to put all these numbers into perspective, but didn't have much luck. Pages and pages of purported health benefit sites, and school experiment protocols, without yielding seemingly reliable results.

 

I know from experience that rosin will attack some metals and metal oxides pretty well, and that's one of the reasons that it's used as a soldering flux. Had to stop using copper when cooking rosin, after I figured out that it produces green varnish with gold-colored specks. :lol:

 

Anyone else?

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EM, that looks like decent varnish there. What's that you are cooking it in and how hot did that batch go? It looks a lot darker than the resin alone did, but I bet it isn't near dark enough to color a violin in thin coats, which is what we want right?

It could probably be mixed with pumice and applied as a ground in 1-2 coats. I wouldn't want to mix any pigments in it as it is way too opaque on it's own. I cooked in a ceramic coated pot at 480-500F. My hot plate was maxed out and would not go any higher. I'm guessing it was on account of the limed rosin. Not nearly dark enough. A thin coat is light golden brown. Not a hint of red which I expected cooking at those temps. So the long cook may have cost a lot of electricity but worth the knowledge gain. Same with liming rosin. I'm out 50-60 bucks but now I won't ever have to go down that path again. If the rosin looks caramelish and or is opaque it will make opaque varnish. No brainer.

Here is the same kind of pot I cook in on Ebay. Lots of them there.

http://www.ebay.com/itm/Le-Creuset-Blue-Cast-Iron-Made-In-France-Sauce-Pan-Pot-Lid-20-/351116664394?pt=LH_DefaultDomain_0&hash=item51c02f1e4a

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Yes I think this will work nicely for a ground varnish. Darker than I expected too. Now I'm anxious to try the low heat blended varnish and trying to preserve that red color in the rosin. Next up I have a lot of oil to wash. Thanks for starting this thread Berl. I learned a lot. Happy slow cookin.

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Ernie, italian literature from the 1700`s mention that the ceramic pot must be new to cook varnish, the explanation is,  once taken to a certain temperature the ceramic becomes full of tiny cracks where the varnish lodges in, and ruins your next batch of varnish.

 

My limed varnishes precipitated and became clear in the pot, perhaps a little precipitation in the jar later on, but not too much, it appears to me that once it begins to precipitate on the jar it is better to let it be for a while, because once the varnish has been poured into another jar it appears that precipitation stopped (or it was a coincidence).

 

Once again early literature mentions these sort of varnishes getting better with time, 20 years is mentioned quite a few times.

 

Good luck!!

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Ernie, italian literature from the 1700`s mention that the ceramic pot must be new to cook varnish, the explanation is,  once taken to a certain temperature the ceramic becomes full of tiny cracks where the varnish lodges in, and ruins your next batch of varnish.

 

My limed varnishes precipitated and became clear in the pot, perhaps a little precipitation in the jar later on, but not too much, it appears to me that once it begins to precipitate on the jar it is better to let it be for a while, because once the varnish has been poured into another jar it appears that precipitation stopped (or it was a coincidence).

 

Once again early literature mentions these sort of varnishes getting better with time, 20 years is mentioned quite a few times.

 

Good luck!!

 

Thank you Carlo for that info. I made the mistake of calling the cooking pot ceramic when it is actually enameled cast iron. Interesting about the ceramic pot though. Makes sense. I think with enameled cast iron. Once the enamel wears offs it's time to buy a new pot but that can take years. I bought mine in a thrift store and the enamel is wearing thin. I will be looking for another one on Ebay.

Grazie

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Your varnish looks real nice on that maple.

Personally, I wouldn't start with anything much redder, red will build , you probably know that.

No I would never start out with a red varnish. I like the ground to be a golden brown and then start building on that. I wasn't expecting this varnish to have as much color. I think it will look OK as a ground varnish. To get to red faster I use two pigments which are very transparent. This sample has three coats of varnish. I don't usually like to apply that much pigment it was just an experiment.

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Thank you Carlo for that info. I made the mistake of calling the cooking pot ceramic when it is actually enameled cast iron. Interesting about the ceramic pot though. Makes sense. I think with enameled cast iron. Once the enamel wears offs it's time to buy a new pot but that can take years. I bought mine in a thrift store and the enamel is wearing thin. I will be looking for another one on Ebay.

Grazie

 

Ernie, you got me now, isn't enameled and ceramic the same thing? It is not wearing off the concern exposed in literature (I have never tried so can not speak out of experience on that) it is as I mentioned above, tiny cracks develop and varnish loges in and remains there until it melts in you next cook damaging your next batch. You can also read some texts asking for a new vitrified pot, which I assume it is enameled or ceramic also...sorry I wish I could be more of help...

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Carlo, I think you're splitting hairs my friend... :) and adding confusion by siting the old manuscripts but please correct me if I'm wrong. A quote that Melvin has made numerous times since I've been on MN which has stuck in my brain is... we are not making boat varnish.

What does that mean exactly?...I'm not sure. But I'm beginning to have an idea how it relates to varnishing a violin.

Cheers

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Ernie, if by boat varnish you mean exterior marine varnish for brightwork, it is spar varnish made with higher fuse point resins, as far as I know not made in new ceramic coated pots, usually high temperature cook as opposed to low temperature rosin varnishes, a very different animal, for that I would recommend the American and British literature from the early 1900's not the italian literature from the 1500, 1600, 1700's.

 

All the best!!!

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