Iron Rosinate

[Don Noon]

I had made up some iron rosinate varnish (in walnut oil) a couple of years ago, and liked the color but never tried it on an instrument until recently, in re-varnishing my VSA viola (I'll post photos eventually on my "bench" thread).  I liked it, although it was very oil-rich and I thought linseed oil would be better.  So I cooked up a new batch, 1:1 and thinned.  On a test maple sample, it looked quite red (yellow to orange in thinner layers), and it seemed like it ended up much redder than when I put it on.  I tested it on a white ceramic tile to check, and it sure does change color when drying. (the lower splotches are old, dry samples)

I only hope it doesn't change back (or worse) over time.  My older iron rosinate doesn't seem to have changed over 2 years (sample test on glass), and Davide had mentioned using iron rosinate with no problem over 20 years, although not in the same type of varnish as mine.

 

 

[Michael_Molnar]

Any details on how you made this rosinate? Did you follow Michelman's process?

BTW, it looks very nice. Kudos.

[Berl Mendenhall]

Don, I don't know how you made your varnish, but I'll explain how I did mine and the results. I made Fulton' s varnish maybe fifteen years ago. In the process of cooking the thick turp. down I added rust to the cook and cooked into a resin. This made a stunning red varnish that was perfectly transparent. I varnished several fiddles with it. I had one of those fiddles come back for a new bridge, I don't remember the specific date, but at least ten to twelve years old. The fiddle was so dark I could hardly see the curl in the maple, very surprised. For what it's worth that was my experience.

[Michael_Molnar]

Berl,

Rust is unstable. The ferric (red) ions eventually switch to black ferrous. You need to secure the ferric state. That I am sure is one of Don's secrets if he indeed has a stable iron rosinate. 

[Don Noon]

No big secret.  The only difference between my resin and the Micheman's process is that I used iron chloride.  Shouldn't be any different as far as the resin goes, just what ions you are left with to wash out.

[David Beard]

In the old writings on dying and coloring that I've seen (just a few, no big survey), iron is mostly used to darken or 'sadden' other colors.  The exception is natural iron oxide earths.  My half baked take away from what I've read is that any actual iron instead of iron oxide will lead to darkening, or even blackening in most any setting.

 

[fiddlecollector]

Did you use only iron chloride for the resinate or a mixture of aluminium,zinc and iron for example? And were you using madder extract or alizarin?

[Davide Sora]

Very nice color, Don.

I did not notice darkening problems with the madder pigments fixed on iron sulphate or the madder / iron rosinate in my lynoxin varnish,  but though I use it sparingly only to cut the reddish color of madder fixed on alum and cochineal.

I believe that even the aging of the pigments or the rosinate before use aid in this sense, because probably has already undergone a preventive oxidation in contact with the air before being used in the varnish.

Speaking with chemists they told me that the iron is actually unstable, but it depends very much on the substances with which it comes in contact with and who might remain stable if the conditions are right. It is a very complex issue, I do not think that there may be a simple answer.

In recent non-invasive studies carried out on the Messiah varnish (I just got the book, reprinted because initially there were errors in the color of the photos ...) the iron peak is always present but they conclude advancing the hypothesis that : "the collocation within the stratigraphy of possible iron oxides is not clearly defined,even though the hypotesis is that they are located close to the preparation layers rather than being dispersed in the varnish".

They also speculate that might arise from the use of natural earths.

Who knows....

[Don Noon]

4 hours ago, fiddlecollector said:

Did you use only iron chloride for the resinate or a mixture of aluminium,zinc and iron for example? And were you using madder extract or alizarin?

Rosin, dissolved with water and potassium hydroxide, precipitated with iron chloride.  That's it, no madder or anything else.

 

4 hours ago, Davide Sora said:

Speaking with chemists they told me that the iron is actually unstable, but it depends very much on the substances with which it comes in contact with and who might remain stable if the conditions are right. It is a very complex issue, I do not think that there may be a simple answer.

Hopefully the dried version of the color will be stable.  My walnut oil version doesn't appear to have changed over 2 years, so that's encouraging.

[Davide Sora]

1 hour ago, Don Noon said:

Rosin, dissolved with water and potassium hydroxide, precipitated with iron chloride.  That's it, no madder or anything else.

Interesting, in my case reacting the rosin with iron sulphate has made a too brown color to be used alone in the varnish.

To obtain an orange brown I had to add the madder extract (Michelman).

Will it be the iron chloride or a different rosin that has made the difference?

[Don Noon]

The precipitate was brown.  Dried, and then dissolved in a solvent, still brown.  Cooked into walnut oil, reddish brown, similarly with linseed oil.  Dried, the linseed version turned much redder, as you can see in the sequence of the first post.  So my conclusion is that the drying oil is the major player in what happens.  It seems like any other perfectly transparent oil color (especially aniline dyes) gets affected when the varnish dries.

[Davide Sora]

5 hours ago, Don Noon said:

The precipitate was brown.  Dried, and then dissolved in a solvent, still brown.  Cooked into walnut oil, reddish brown, similarly with linseed oil.  Dried, the linseed version turned much redder, as you can see in the sequence of the first post.  So my conclusion is that the drying oil is the major player in what happens.  It seems like any other perfectly transparent oil color (especially aniline dyes) gets affected when the varnish dries.

At what temperature and for how long did you cooked the oil with the resin to make the varnish?

I have had some bad experience cooking the rosinate in the oil varnish going over 100/120° C approximately, the color has faded almost completely.

Well, the rosinate was madder/zinc and not madder/iron, an intense red reduced to an insignificant pale orange after cooking.

 

[Don Noon]

I could imagine that cooking a madder-based color would not like high temperatures.  My sequence for cooking the iron rosinate was to gradually raise the temperature to 250C (setting on the pot thermocouple; bulk varnish temperature probably 20C less) and hold for 1/2 hour or slightly longer.  In the past I tried cooking zinc/alizarin rosinate into oil, and it didn't seem to want to stay there.  It kept precipitating out.  I also made some iron/alizarin varnish, and it's purple.  These other varnishes were quite a while ago and I don't have good records of what I did.

I just checked my iron rosinate varnish, and there doesn't seem to be anything building up on the bottom of the jar.  So far, so good.

[Davide Sora]

17 minutes ago, Don Noon said:

I could imagine that cooking a madder-based color would not like high temperatures.  My sequence for cooking the iron rosinate was to gradually raise the temperature to 250C (setting on the pot thermocouple; bulk varnish temperature probably 20C less) and hold for 1/2 hour or slightly longer.  In the past I tried cooking zinc/alizarin rosinate into oil, and it didn't seem to want to stay there.  It kept precipitating out.  I also made some iron/alizarin varnish, and it's purple.  These other varnishes were quite a while ago and I don't have good records of what I did.

I just checked my iron rosinate varnish, and there doesn't seem to be anything building up on the bottom of the jar.  So far, so good.

Thanks for the infos, I will have to give a try to my old Iron sulfate rosinate, if i only remember were is it.....

[Luis Martins]

Some theory regarding the crystallization of amorphous iron oxide nanoparticles

The precipitation method in this paper is quite different but results in smaller particles than the chemical precipitation.

It may suggest that iron oxide may crystallize to some form of hematite during the cooking process of the iron precipitate with the organic compounds (cooking the varnish), turning the resulting Fe into a non reactive, stable ovoid shaped crystal. But it will need time and temperature. Some studies say 400h@100C. Increasing temperature should decrease time.

It may also contribute to some iridescence in the varnish since crystallized iron flakes diffract light.

If Fe does in fact crystallize in the process of cooking the varnish, it would take trace amounts of Fe to produce real results, something like 0,5 to 1%

[Davide Sora]

20 hours ago, Luis Martins said:

Some theory regarding the crystallization of amorphous iron oxide nanoparticles

The precipitation method in this paper is quite different but results in smaller particles than the chemical precipitation.

It may suggest that iron oxide may crystallize to some form of hematite during the cooking process of the iron precipitate with the organic compounds (cooking the varnish), turning the resulting Fe into a non reactive, stable ovoid shaped crystal. But it will need time and temperature. Some studies say 400h@100C. Increasing temperature should decrease time.

It may also contribute to some iridescence in the varnish since crystallized iron flakes diffract light.

If Fe does in fact crystallize in the process of cooking the varnish, it would take trace amounts of Fe to produce real results, something like 0,5 to 1%

 

On 1/2/2017 at 11:30 AM, Davide Sora said:

Speaking with chemists they told me that the iron is actually unstable, but it depends very much on the substances with which it comes in contact with and who might remain stable if the conditions are right. It is a very complex issue, I do not think that there may be a simple answer.

Here we are, I told you.......

I tried to read the paper but it is far too complex for my limited knowledge of chemistry, so I gave up.

However your suggestion it's very interesting, maybe heat induced nano-particles have something to do with color in colophony cooking, I recall someone (Nagyvary?) found the presence of nano particles for the yet unidentified base color of the colored Stradivari's varnish.

[Don Noon]

I too tried reading the paper, and it's way beyond my level of chemistry.

However, I don't see that there is anything in the paper that would explain why the color of the varnish changes only when drying.  The iron rosinate was consistently brown all the way through the sequence of precipitation and cooking, but only changed when drying at ambient temperature.

[Janito]

Hypothesis:

(i) Iron rosinate particles of irregular shape present a multitude of surfaces to incident light. The light is reflected/defracted in a highly unstable way when the particles move around in suspension in the liquid medium.

(ii) The reflection/diffraction pattern becomes more stable when the movement of the particles is greatly reduced when they are caged in the non-mobile ('dry') varnish medium.

(iii) The colour changes between 'wet' and 'dry' varnish.

[Berl Mendenhall]

Fascinating topic, the transparency and beautiful red of Don's varnish is very enticing.   

  

[Luis Martins]

1 minute ago, Janito said:

Hypothesis:

(i) Iron rosinate particles of irregular shape present a multitude of surfaces to incident light. The light is reflected/defracted in a highly unstable way when the particles move around in suspension in the liquid medium.

(ii) The diffraction pattern becomes more stable when the movement of the particles is greatly reduced when they are caged in the non-mobile ('dry') varnish medium.

It might also mean that not all Fe is in a crystalline form, therefore reactive. But the above is a good explanation.

I suggest a new approach by implementing the "gesso" technique using TiO2 (titanium dioxide, or titanium white) powder to prepare the wood for the iron based varnish. Or any other varnish for that matter.

TiO2 is a well established anti fungal/bacterial product, and has great reflective properties, so not only will help prevent decomposition on the wood surface but the residual leftover particles after air cleaning or dusting off, will help in the enhancement of the refractive/reflective properties of the iron based varnish due to stratification. This process might explain the Titanium content of some instruments varnish, or wood surfaces, and their highly reflective/refractive properties. I'm also assuming that in the 1700 they couldn't tell the difference between "gesso" powder, or titanium dioxide powder, or if they were mixed together at some level.

[joerobson]

5 hours ago, Davide Sora said:

 

the yet unidentified base color of the colored Stradivari's varnish.

Is positively identified as cochineal.....

on we go,

Joe

[Davide Sora]

28 minutes ago, joerobson said:

Is positively identified as cochineal.....

on we go,

Joe

Brandmair & Greiner bet more on the vermilion (cinnabar) but they have also found other pigments like madder and cochineal and some others black and green.

But the conclusion is that they are not those who give the main color.

[joerobson]

David,

True as far as the Brandmair study is concerned.  The J.P.Echard work goes into more detail.  It is also VERY true that there are many additives which vary from instrument to instrument giving differing appearances to individual instruments. The cinnabar,given quantity and particle size and distribution reminds me of retouch...but that is a question yet to be resolved.  The basic red lake has been isolated as cochineal....tentatively by Brandmair and positively by Echard.   There is also strong presence of iron oxide, though not in the quantity that would dictate this being the primary colorant.

Don...sorry I did not mean to highjack your thread!!!!

on we go,

Joe

 

[Davide Sora]

Yes,  I know that cochineal is the more frequently found pigment, but I agree with Greiner and Brandmair that the little quantity dos not make the main color of the colored varnish, I don't remember Echard thoughts in this regard.

[nathan slobodkin]

Don just picking up on something in your posts. Do you have a varnish pot that can be rheostat controlled up to 250C? Is that something commercial or did you make it?