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Working with pigments


Jim Bress
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On 5/26/2018 at 7:26 AM, Michael Darnton said:

Not true. The classical example of the is lapis luzuli, which is basically opaque: grind it too much and it turns into even more opaque grey mud. Every pigment has its optimum size, if you are looking for transparency, but remember that this is not something that painters were generally looking for, so you need to go deeper into the subject than to, for instance, read painting books.

I think someone already mentioned the necessity of getting the color close to the wood (compare to reading a newspaper through wax paper). Another important component is compatibility of the layers. A ground can look cloudy, but the right varnish on top will make it look clear, and the reverse. I personally think that the very first thing that touches the wood is the most important layer.

Someone commented earlier that iron pigments aren't transparent. Also not true. There are transparent ones, but very few. I have always been fascinated by the idea that iron pigments are essentially local, and this hole might have something completely different from the one a mile away. Look at the many examples that historical pigment suppliers sell. What if there was one particular pigment from one specific hole that worked well that all the violin makers had access to? I've spend a lot of $$$ on this, and my thought is that all the ones you can buy now are ground too fine, so I might have walked right over it. I guess the next step is for me to try to make my own. . . .

Thanks for the input Michael.  I plan on trying the colored varnish directly over the ground or one layer above that, both topped with two more thin layers.  That's the plan anyway.  Plenty of testing before anything touches the viola.  Then adjust because things still have a way of not going quite as planned.  :)

-Jim

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On 5/25/2018 at 11:15 PM, CSchabbon said:

And those Cinquasia colors are great for retouch. I personally wouldn't use them for new instruments though.

 

On 5/26/2018 at 7:35 AM, arglebargle said:

Why?

Seeing as I already bought some, your insight on why not to use Cinquasia colors in new making would be appreciated.

-Jim

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On 5/26/2018 at 7:26 AM, Michael Darnton said:

Not true. The classical example of the is lapis luzuli, which is basically opaque: grind it too much and it turns into even more opaque grey mud. Every pigment has its optimum size, if you are looking for transparency, but remember that this is not something that painters were generally looking for, so you need to go deeper into the subject than to, for instance, read painting books.

I think someone already mentioned the necessity of getting the color close to the wood (compare to reading a newspaper through wax paper). Another important component is compatibility of the layers. A ground can look cloudy, but the right varnish on top will make it look clear, and the reverse. I personally think that the very first thing that touches the wood is the most important layer.

Someone commented earlier that iron pigments aren't transparent. Also not true. There are transparent ones, but very few. I have always been fascinated by the idea that iron pigments are essentially local, and this hole might have something completely different from the one a mile away. Look at the many examples that historical pigment suppliers sell. What if there was one particular pigment from one specific hole that worked well that all the violin makers had access to? I've spend a lot of $$$ on this, and my thought is that all the ones you can buy now are ground too fine, so I might have walked right over it. I guess the next step is for me to try to make my own. . . .

Not only particle size, but the amount you put into a specific volume. I have heard no discussion of the density of the particulate, which would make a significant difference. Quite a bit of speculative discussion of microscopic particles(excuse me, I am a physicist).

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On 6/5/2018 at 7:29 AM, Jim Bress said:

 

Seeing as I already bought some, your insight on why not to use Cinquasia colors in new making would be appreciated.

-Jim

One reason personally don't like it, the varnish will show up as dark blue/nearly black in the blacklight. It's ok for retouch, since it will make it easier for the next person working on the instrument separating retouch from original varnish. If you don't mind, its probably fine to use in new making.

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I am intrigued with Kremer's Meteorite Brown (10975) although I do not like the idea of destroying these remnants of our solar system's birth. I am toying with the idea of incorporating a smidgen into my varnish in recognition of my profession. :)

 

"Our meteorites were found near the Moroccan town of Zagora. These Chondrites belong to the so-called stone meteorites and are about 4.5 billion years old. The meteorite fragments are ground to a powder finer than 80 µ."

 

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40 minutes ago, Michael_Molnar said:

I am intrigued with Kremer's Meteorite Brown (10975) although I do not like the idea of destroying these remnants of our solar system's birth. I am toying with the idea of incorporating a smidgen into my varnish in recognition of my profession. :)

 

"Our meteorites were found near the Moroccan town of Zagora. These Chondrites belong to the so-called stone meteorites and are about 4.5 billion years old. The meteorite fragments are ground to a powder finer than 80 µ."

 

Sounds gimmicky, but it works for you.  At 4.5 billion years old it could be a piece of Theia.   I guess you can't call it an Earth pigment.  :P

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2 hours ago, Michael_Molnar said:

I am intrigued with Kremer's Meteorite Brown (10975) although I do not like the idea of destroying these remnants of our solar system's birth. I am toying with the idea of incorporating a smidgen into my varnish in recognition of my profession. :)

 

"Our meteorites were found near the Moroccan town of Zagora. These Chondrites belong to the so-called stone meteorites and are about 4.5 billion years old. The meteorite fragments are ground to a powder finer than 80 µ."

 

You might want to determine if it has free iron in it.  If so it is very likely to darken if used as a colorant.

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On 5/26/2018 at 2:26 PM, Michael Darnton said:

 A ground can look cloudy, but the right varnish on top will make it look clear, and the reverse. I personally think that the very first thing that touches the wood is the most important layer.

I agree, not the best example below, photos taken in the same light and place

VarnishGroundTest.thumb.jpg.30bf10bc1c91f392d3956415a4ed2a55.jpg

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On 5/26/2018 at 7:26 AM, Michael Darnton said:

Not true. The classical example of the is lapis luzuli, which is basically opaque: grind it too much and it turns into even more opaque grey mud.

Could be. Have you come up with a solid way of differentiating between the optical effect of reduced pigment particle size, and the increase in contaminants which come from the grinding vessel and grinding media, as grinding time increases?

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2 hours ago, David Beard said:

You might want to determine if it has free iron in it.  If so it is very likely to darken if used as a colorant.

I wouldn't really add this stuff to my varnish. The iron in meteorites is chemically active. In fact, I do not use any iron in my varnish because it is unpredictable. Some makers get excellent results, nevertheless. 

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4 hours ago, David Beard said:

I'm very comfortable using natural earth iron oxide colors. I figure the natural stuff has been in an oxidizing environment long enough. Besides, we have successful permancy tests running back to cave painting.

But I'm otherwise shy about using iron.

1

Here is a quote from Maximilian Toch - Materials for Permanent Painting:

Madder lake may be mixed with any oxide of iron color which has been burnt, but may not be mixed with any raw iron color. For instance, madder or alizarin may be mixed with Indian red, forming a color known as Tuscan red, which is perfectly permanent. It may also be mixed with burnt sienna, burnt ochre, burnt umber, etc., but is fugitive when mixed with raw ochre, raw sienna or raw umber. The chemical colors like flake white (white lead), zinc oxide, chrome yellow, Naples yellow and chrome green all bleach it, but colors like quick silver, vermilion, cadmium yellow and all of the blacks do not affect it. The safest way in which to use it is as a glaze over a ground which is thoroughly dry. Madder lake deepens considerably when placed in a dark place, but is revived when subjected to bright sunlight.

 

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17 minutes ago, Michael_Molnar said:

Here is a quote from Maximilian Toch - Materials for Permanent Painting:

Madder lake may be mixed with any oxide of iron color which has been burnt, but may not be mixed with any raw iron color. For instance, madder or alizarin may be mixed with Indian red, forming a color known as Tuscan red, which is perfectly permanent. It may also be mixed with burnt sienna, burnt ochre, burnt umber, etc., but is fugitive when mixed with raw ochre, raw sienna or raw umber. The chemical colors like flake white (white lead), zinc oxide, chrome yellow, Naples yellow and chrome green all bleach it, but colors like quick silver, vermilion, cadmium yellow and all of the blacks do not affect it. The safest way in which to use it is as a glaze over a ground which is thoroughly dry. Madder lake deepens considerably when placed in a dark place, but is revived when subjected to bright sunlight.

 

Maybe I should be more cautious about using raw earth colors then, at least in direct combination with madder lake.

I haven't read Toch.  Though I do have a copy of his nephew Mayer's book.

Madder was regarded traditional as potentially fading. And somewhere I read this is part of why it's common in classical painting to find a passage of madder lake supported with other reds underneath or in combination.  But I'm certainly not expert on these points.

I have trouble trusting modern authors on pigments.  They so often show a bias toward the lab scientist's or chemical engineers viewpoint.  And frankly I'm highly biased toward the artisan practitioner's viewpoint.

The industrialization and commercialization of paint, pigment, and varnish products was big money. People were inventing new colorants, but also making claims the colors that have held up for centuries in countless art works were inferior and fugitive.

Particularly for the very narrow purpose of trying to get understanding of classical violin varnish, I've been much more drawn to very old statements about how to use the traditional materia succesfully rather than modern statements about why not to use them.

A statement like you quoted from Toch is interesting. And perhaps relevant. But I'd also like to know if his statement applies to natural raw earths or only synthetic ones? There was a tendancy to act like such materials are fully equivalent. 

Anyway, it's interesting.  Happily, the burnt versions are often more useful for our work anyway, as the tend to be more red brown and more semi-transparent.

Ugh. Now I'll have to read Toch.

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The science of turning a cloudy ground into a transparent layer goes like this:

The ground must be a chemical that is fundamentally transparent when in a smooth, crystalline form. When in powder form, it may appear cloudy because the facets of the small grains are oriented in many random directions that bend the light into unfocused directions. But if you used a microscope to view the individual grains, you would see that they are transparent.

The varnish applied over the ground must have an index of refraction close to the index of the ground material itself. This effectively stops the light from being bent in random directions and causes the cloudy  ground to turn transparent.

For example, some famous makers on this forum have posted that they use calcium sulfate (gypsum) or calcium hydroxide (slaked lime) as a mineral ground. Both of these minerals are clear, colorless crystals with a refractive index of about 1.56. Various application methods leave the wood looking like it is covered in a dense white powder. Applying a thin layer of shellac, with is refractive index of about 1.53, or some linseed oil varnishes with resin content, also with refractive indexes of 1.5ish, make the cloudy ground turn transparent and the underlying detail of the wood grain appear.

I have used the gypsum/shellac methods and it works very well with gypsum of high purity.

Any colored mineral that is essentially transparent in crystalline form can also be used as a ground if one covers the ground layer with a smooth varnish layer with similar refractive index.

The term pigment is typically used for a mineral color that is opaque. The science of getting a "transparent" varnish from opaque particles is rather complex but I think it has been covered in previous posts.

 

 

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1 hour ago, ctanzio said:

The science of turning a cloudy ground into a transparent layer goes like this:

The ground must be a chemical that is fundamentally transparent when in a smooth, crystalline form. When in powder form, it may appear cloudy because the facets of the small grains are oriented in many random directions that bend the light into unfocused directions. But if you used a microscope to view the individual grains, you would see that they are transparent.

The varnish applied over the ground must have an index of refraction close to the index of the ground material itself. This effectively stops the light from being bent in random directions and causes the cloudy  ground to turn transparent.

For example, some famous makers on this forum have posted that they use calcium sulfate (gypsum) or calcium hydroxide (slaked lime) as a mineral ground. Both of these minerals are clear, colorless crystals with a refractive index of about 1.56. Various application methods leave the wood looking like it is covered in a dense white powder. Applying a thin layer of shellac, with is refractive index of about 1.53, or some linseed oil varnishes with resin content, also with refractive indexes of 1.5ish, make the cloudy ground turn transparent and the underlying detail of the wood grain appear.

I have used the gypsum/shellac methods and it works very well with gypsum of high purity.

Any colored mineral that is essentially transparent in crystalline form can also be used as a ground if one covers the ground layer with a smooth varnish layer with similar refractive index.

The term pigment is typically used for a mineral color that is opaque. The science of getting a "transparent" varnish from opaque particles is rather complex but I think it has been covered in previous posts.

 

 

Any estimate of how much RI difference would be give a nearly transparent, but somewhat refractive result. Seems to me it's more visually interesting if the light is kicked around a bit, but not too much.   If the RI match is too good this effect would vanish.   Thoughts????

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7 hours ago, David Beard said:

Any estimate of how much RI difference would be give a nearly transparent, but somewhat refractive result. Seems to me it's more visually interesting if the light is kicked around a bit, but not too much.   If the RI match is too good this effect would vanish.   Thoughts????

I discussed this in my VSA talk of a few years back. RI difference is a red herring in most cases. The issue is the attachment or wetting of the varnish/oil to the pigment surface. It there is a gap, the RI difference is huge and scattering or reflection at the gap increases dramatically. This is why you want to mull and mull well. Or, you can use a dispersant, but I do not recommend that unless you are working with nano-pigments. According to some pundits, the ionic makeup of the linseed oil used for mulling is key to wetting the pigment. See Natural Pigments website for lots of informative articles.

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That's not what I'm asking. 

Doesn't anyone know how much RI difference (when well wetted) will still give a desirable amount of scattering?  

I want the light to dance a bit. And that won't happen if the RIs match too well.  So with transparent particles how much RI difference gives light play, but doesn't totaly lose too much transparency?

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1 hour ago, Michael_Molnar said:

I discussed this in my VSA talk of a few years back. RI difference is a red herring in most cases. The issue is the attachment or wetting of the varnish/oil to the pigment surface. It there is a gap, the RI difference is huge and scattering or reflection at the gap increases dramatically. This is why you want to mull and mull well. Or, you can use a dispersant, but I do not recommend that unless you are working with nano-pigments. According to some pundits, the ionic makeup of the linseed oil used for mulling is key to wetting the pigment. See Natural Pigments website for lots of informative articles.

In metallic guitar finishes,which are just old nitrocellulose lacquer car finishes, much is talked about the flop agents, which provide preferential orientation of metal flakes in gravity, this study goes in depth in trying to create terminology and to distinguish different qualities of refractance created, how would the idea of a dispersent or flop agent correlate with traditional varnishes?

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1 hour ago, David Beard said:

That's not what I'm asking. 

Doesn't anyone know how much RI difference (when well wetted) will still give a desirable amount of scattering?  

I want the light to dance a bit. And that won't happen if the RIs match too well.  So with transparent particles how much RI difference gives light play, but doesn't totaly lose too much transparency?

The simplified equation ignores acute incidence and polarization:

{\displaystyle R=\left|{\frac {n_{1}-n_{2}}{n_{1}+n_{2}}}\right|^{2}}.

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