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GlennYorkPA

Stradivari's Ground

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The recently issued Vol XXI No. 1 Journal of VSA Papers contains two interesting papers relating to the structure and composition of the ground asnd varnish of Cremonese instruments of the classical period.

Having spent several hours attempting to understand just these two papers, and for the benefit of those who have not read them, I'd like to share what I extracted from them.

Beginning with the second paper by Harris, Sheldon & Johnston -A Recreation of the Particulate Ground Varnish Layer Used on Many Violins Before 1750 - the authors end with some very useful definitions.

Recognising that there is much confusion between the terms varnish, fillers, sealers, grounds and varnishes, the authors carefully point out that what they are referring to is a layer 35 microns thick (that's almost as thick as a sheet of paper), that does not penetrate the wood but lies on top of it and seals the open pores of the wood capillaries.

To call it a filler or a sealer would be misleading because these substances are usually much thinner.

As they say, 'a ground is the stuff one sees when the top varnish layer wears off an instrument made in the classical era'.

The title of their article contains the word 'particulate' to recognise the fact that these classical grounds contain particles.

This paper relates to the previous paper by Bruce Tai titled: Stradivari's Varnish: A Review of Scientific Findings -Part 1.

This major review of all literature, historic and scientific, with 94 references, covers both ground and varnish of Stradivari's violins. Much of this review concerns the upper, colored, varnish layer. It appears that particles are abundant in most of the layers making up the complete wood finish and this makes it a little comfusing as does the fact that other makers apart from Stradivari are mentioned.

There seems to be some agreement that it is the lower, ground layer that most contributes to the tonal properties of the instrument which is why Harris & Sheldon tried to recreate it.

In a section subtitled: Further Considerations about the mineral ground, Tai notes that the most abundant particles to have been detected in Strad's ground are: Calcite, potassium feldspar, Gypsum and quartz. All are naturally occuring and of such a fine particle size that when dispersed in an organic matrix, the result is transparent. Apparently the particles are in the 0.5 - 2.0 microns.

Now comes speculation on how these small sizes were obtained with the conclusion that 'how powders of such finenes were prepared in 17thC Italy deserves further investigation.......'

Sooooooo, back to the Harris & Sheldon article, they formulate what they aptly call the 'Harris & Sheldon' emulsion ground varnish. It consists of an oil-resin mix, emulsified with glue and stabilized by clay-sized mineral particles (kaolin). They end up with a goop the consistemcy of mayonaise and apply it with the thumb. (Oh yes, epithelia/skin flakes are also found in Strad's ground indicating it was applied using the bare hand rather than a brush).

Apparently the result of applying this to wood strongly resembles an Andrea Amati violin in Charles Beare's collection from which the top varnish has been removed. It has a low sheen and slightly chalky appearance.

Glenn

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There are some pictures of Harris and Sheldon's violins on their website. Folk can judge for theselves how 'Cremonese' they look

http://www.violin.uk.com

When folk talk about varnish discoveries they have made I like to see how they put it into practice and some results before I take too much notice. Were there pictures with their article?

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Incidental question Melvin but can you point to anyone who is using a mineral ground of the indicated composition which you feel comes close to looking right?

Don't mean to put you on the spot so feel free to ignore the question entirely. :)

Photos are only going to show us that someone is in the ballpark anyway, you can't really tell without seeing an instrument in person in 3D.

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Hi Melvin,

Violin varnish has so many different aspects to it . It's entirely possible that the writers have nailed the properties of the ground layer but haven't quite mastered the coloration or patina of the varnish. I think they should be accorded some leeway.

Oded

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Incidental question Melvin but can you point to anyone who is using a mineral ground of the indicated composition which you feel comes close to looking right?

Don't mean to put you on the spot so feel free to ignore the question entirely. :)

Photos are only going to show us that someone is in the ballpark anyway, you can't really tell without seeing an instrument in person in 3D.

Andres, can you say a few things about what a ground should look like? I will assume that the wood is wetted somehow to make the grain very visible, or is there something else? Do you mean a ground where the upper varnish is worn off, or a ground that has no upper varnish. (may not be the same thing) I meant a ground that you put on and before any other varnish added.

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John, I'm thinking of the ground's effect on how the wood looks, i.e. not necessarily the texture of the ground where varnish has worn away. This latter is perhaps more what Melvin is thinking of?

As to how it looks, yes the wetting effect. I can't do better than Michael Darnton's comparison of the effect to a holograph, particularly as I have seen precious few examples in person.

About what a ground 'should' look like--I'm not here to argue that the way the best Cremonese grounds look is the only way to go. I just take it as a given, in these discussions about what they did, that the visual effect is at least part of why we're talking about it.

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John, I'm thinking of the ground's effect on how the wood looks, i.e. not necessarily the texture of the ground where varnish has worn away. This latter is perhaps more what Melvin is thinking of?

As to how it looks, yes the wetting effect. I can't do better than Michael Darnton's comparison of the effect to a holograph, particularly as I have seen precious few examples in person.

About what a ground 'should' look like--I'm not here to argue that the way the best Cremonese grounds look is the only way to go. I just take it as a given, in these discussions about what they did, that the visual effect is at least part of why we're talking about it.

Thanks Andres... As to wetting effect only, I find that for me, xylene on the wood makes it look the most wet. I have tried to use various solvents just as a test. The RI of xylene is very close to that of wood, it seems. Turpentine also looks wet, but perhaps not quite as much.

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I think it is extremely possible that the ground looked rather different as applied compared to when the varnish is worn off.

Yes, various emulsions can have more or less porosity to absorb some overcoat. That is why I asked in that manner.

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I think it's interesting that many minerals that enter the pores actually "lock" the flame. You don't get the depth nor refraction. Might have to order some kaolin clay and give this a shot and add to the photos i'm putting together.

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Incidental question Melvin but can you point to anyone who is using a mineral ground of the indicated composition which you feel comes close to looking right?

Don't mean to put you on the spot so feel free to ignore the question entirely. :)

Photos are only going to show us that someone is in the ballpark anyway, you can't really tell without seeing an instrument in person in 3D.

...............................................

Hi Andres.

I can't really talk about makers grounds I like in any meaningful way without breaking confidences in the few cases where I know what is or is not being used. I think you guessed that anyway. :)

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I think it's interesting that many minerals that enter the pores actually "lock" the flame. You don't get the depth nor refraction. Might have to order some kaolin clay and give this a shot and add to the photos i'm putting together.

..........................................................

If we look at the ground in terms of materials we think we understand it can act as an optical illusion. There is a lot of stuff from the optics of layers etc that confuses the eye I think.....

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I have tried plaster of paris in the gound coats and found it hid the flame to much.......maybe the quantity was to great

does anyone do this with success ?

Adam,

You can't just use plaster of Paris willy nilly. What the authors are pointing out in the articles I cited is that the particle size found in the ground of Cremonese instruments is extremely small, in fact smaller than it is thought possible to achieve by grinding powders.

If the refractive index of the particles matches precisely the RI of the binder, it doesn't matter what the particle size is but the greater the difference in RI, the smaller the particles must be to avoid scattering. In the Italian instruments studied, the particles were so small they were only discovered by electron microscopy because they couldn't be seen with visible light.

Glenn

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In a section subtitled: Further Considerations about the mineral ground, Tai notes that the most abundant particles to have been detected in Strad's ground are: Calcite, potassium feldspar, Gypsum and quartz. All are naturally occuring and of such a fine particle size that when dispersed in an organic matrix, the result is transparent. Apparently the particles are in the 0.5 - 2.0 microns.

Glenn

Glenn, Are the minerals infered from elemental breakdown or by actual x-ray diffraction or some other method to find particular crystal types?

"b-sharp' had some very good ideas here. Mike Molnar is an astronomer and likely has something to say about glass grinding. I am sure there were glass grinders nearly everywhere. Window glass could not be cast optically flat could it? We know that someone saw Stradivari working all day at his bench and had on a white leather apron. This observer must have looked through a window......... Somehow good thread fizzle out and things are lost to future discussions.

http://maestronet.com/forum/index.php?showtopic=318649

Down the page a bit. 'b-sharp' has the mayonaise already, the existing idea of a tempera/oil varnish with ground minerals instead of colored pigments. It was the tempera/oil varnish which was supposedly used before pure oil varnishes. Van Eyke brothers can be googled.

:) ******************************************************************************** :)

TRY IT ONCE AND FOR ALL .....

I am willing to emulsify any samples sent to me. The only expense is shipping and the cost of the plastic bottles I use. These are under $2, nice Nalgene laboratory grade. I buy them in bulk because standardized containers help the process.

If anyone wishes to send a sample, 3oz or 100cc is adequate. To much less is not convenient but possible. Please contact me. I can tell you now that they will be the viscosity of thin oil paint *, not mayonaise. Multiple layers can be brushed wet on wet, provided previous coats air for 15 minutes or so. I spray, but two or three thin brush coats should be equivalent.

The above was to avoid the complaint that Strad could not spray coat. Brushing is possible to overcome that objection. Also, the minerals are quite fine. I will include a glass plate coated so that you can see what it looks like. Send a wood sample if you wish me to do anything with it. Send instructions, of course.

All materials used (except your varnish maybe :) was available in Strad's day. And also simple to produce or collect. 3 oz of your varnish likely costs me less than 50cents to make 6 oz of emulsion for you.

One more thing please.... Tell me if you are looking for what Strad USED or something that is physically indistinguishable except with laboratory methods such as Nagyvary uses........... It seems to me that the desire to know exactly WHAT is from the need to know if it was plausible. Believe me, it IS plausible. You will see when you get back your stuff.

I would like to do this to convince you people. If you have $100 per 10cc varnish, don't bother. You probably got ripped off in the first place.

* They even look like thin oil paint, but they are really oil in water. All brushes and dishes water-wash.

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I have tried plaster of paris in the gound coats and found it hid the flame to much.......maybe the quantity was to great

does anyone do this with success ?

Glenn, I went through the process of "washing" Plaster of Paris. Mix with lots of water, stir, let settle, stir, settle, stirr, let settle, pour off the clear water, add water, etc. All this over a period of weeks.

Next, add lots of water and let settle for only a short time and pour the milky water off. This milky water will contain finer particles. Use these.

John

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***************************************************************** :)

TRY IT ONCE AND FOR ALL .....

I am willing to emulsify any samples sent to me. The only expense is shipping and the cost of the plastic bottles I use. These are under $2, nice Nalgene laboratory grade. I buy them in bulk because standardized containers help the process.

If anyone wishes to send a sample, 3oz or 100cc is adequate. To much less is not convenient but possible. Please contact me. I can tell you now that they will be the viscosity of thin oil paint *, not mayonaise. Multiple layers can be brushed wet on wet, provided previous coats air for 15 minutes or so. I spray, but two or three thin brush coats should be equivalent.

The above was to avoid the complaint that Strad could not spray coat. Brushing is possible to overcome that objection. Also, the minerals are quite fine. I will include a glass plate coated so that you can see what it looks like. Send a wood sample if you wish me to do anything with it. Send instructions, of course.

All materials used (except your varnish maybe :) was available in Strad's day. And also simple to produce or collect. 3 oz of your varnish likely costs me less than 50cents to make 6 oz of emulsion for you.

One more thing please.... Tell me if you are looking for what Strad USED or something that is physically indistinguishable except with laboratory methods such as Nagyvary uses........... It seems to me that the desire to know exactly WHAT is from the need to know if it was plausible. Believe me, it IS plausible. You will see when you get back your stuff.

I would like to do this to convince you people. If you have $100 per 10cc varnish, don't bother. You probably got ripped off in the first place.

* They even look like thin oil paint, but they are really oil in water. All brushes and dishes water-wash.

Wow. How generous of you. I will send you some. Hope you are not swamped.

John

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It certainly is generous of John to volunteer his services but frankly I don't see what the fuss is all about, you slowly add the resin, oil or varnish to the liquid with emulsifier (glue, gum arabic, casein, egg, burnt honey etc), stir (with a stiff brush is better) until they combine into an opaque liquid. You can control how thick it is , from mayonnaise to water, by diluting with water.

The worse that can happen is that it won't succeed and you throw it out-it won't set your house on fire, or drive you out with horrible smells or explode :)

It isn't any more difficult than making chocolate milk (which also contain emulsifying agents) IMHO

Oded

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