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Old 04-08-17, 07:50 PM
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vermillion9 vermillion9 is offline
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Default NP Tempera Ground

I'm looking with interest at Natural Pigments Tempera Ground. I'd like to buy some but am unsure of how much to buy. The jars come in 8, 16, and 32 ounces; does anyone know how far it goes? Like, "8 oz covers 1 sq ft with 4 coats" kind of thing. Any advice is appreciated.
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Old 05-08-17, 06:14 PM
Georgeoh Georgeoh is offline
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It is difficult to provide such information because it is entirely dependent upon how thickly each coating is applied and the type of support to which it is applied. Based upon our own testing we had the following results on hardboard:

The first coat will absorb into the hardboard and will require a lot more product than the second coat, where absorbency is lessened. In our testing, it took approximately 0.5 fluid ounce of Rublev Tempera Ground to cover one square foot of hardboard for the first coat, which is approximately 250 square feet per gallon. It took less than half that amount for the second coat, which is approximately 500 square feet per gallon. Applying additional coats will require slightly less ground for each coat.
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Old 05-08-17, 08:24 PM
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vermillion9 vermillion9 is offline
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Thanks! That's helpful information.
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Old 05-08-17, 09:07 PM
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Koo Schadler Koo Schadler is offline
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By the way, this ground also works really well for metalpoint drawing. I've just coated several MDF panels as well as some 300# watercolor paper with it, tinted in various colors. I started with a relatively thick layer but applied successive layers thinner and thinner, each one a slightly different hue, all adding up to a beautifully rich surface (akin got what Victor Koulbak creates in his drawing, for those of you who know his work). In the past I've used homemade traditional gesso for metalpoint; the benefits of using the Natural Pigments Tempera Ground is its convenience (comes in a jar!) and doesn't need to be warmed.

Koo

Last edited by Koo Schadler; 05-08-17 at 09:13 PM.
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Old 05-08-17, 09:16 PM
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Koo Schadler Koo Schadler is offline
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Another question for George about this ground: is it correct to presume that at some point it will cure and no longer be water soluble? I am wet sanding the surface of the panels I just made, which is nicely dissolving and redistributing the ground to create a very smooth surface - but at some point will it no longer respond to wet sanding (aside from being abraded)?

Thanks,

Koo
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Old 07-08-17, 01:12 PM
dbclemons dbclemons is offline
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Their website advises against using this on a flexible surface, such as canvas (or paper) even if mounted to board beforehand, in order to avoid potential cracking. Doesn't mean you can't, but it's your risk. There's also advice to prepare the board first with two coats of acrylic medium (their Fluid Medium or Golden's GAC100 would work) to avoid discoloration, but that should also allow you to apply the first coat more thinly.
https://www.naturalpigments.com/tempera-ground.html
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Old 08-08-17, 01:16 PM
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Koo Schadler Koo Schadler is offline
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Thanks for that info, DB. I think the lack of flexibility in this ground is due more to its solid content (high PVC), not any brittleness in the binder, but I'm not sure. It would seem if paper is applied to a solid support that would prevent cracking, so I'm curious why it's advised against...but George will explain it.

To clarify "discoloration": an initial application of Natural Pigment's Fluid Medium or Golden GAC 100 is to prevent SID (support induced discoloration), in which impurities in a wood based support are drawn up into a water based ground, discoloring it. So I don't think it applies to white paper, but I'm not sure. And perhaps there might be other reason to prepare paper with an initial coating as well; i.e. reduce paper's absorbency so fewer coats of the Tempera Ground are needed (since, for a metalpoint drawing I'm just trying to create a surface with tooth, not a substantial ground that will absorb the water content in tempera paint).

Anyhow, for me all this adds up to questions for George -

1. Is the concern of cracking due solely to the high solid content in the Tempera Ground, or also a consideration of the binder?

2. Why is backing a flexible support with a solid support (paper on wood panel) potentially not enough to prevent cracking?

3. Any reason(s) to coat paper with either the Fluid Medium or GAC 100 when using NP's Tempera Ground as a base for metalpoint drawing?

4. I'm thinning Tempera Ground with water when building up multi-colored layers for a drawing because I want to apply the thinnest possible layer. The Natural Pigment's website says don't thin more than 20% with water, further dilution can be achieved with the Fluid Medium. What are the consequences of adding too great a percentage of water to the ground - underbound, cracks, flaking?

5. And, my earlier question - at some point does the ground cure and is no longer water soluble (and thus not affected by wet sanding)?

Thanks as always George! You are a fount of knowledge for the tempera community and one of the few manufacturer's creating products for egg tempera artists, which I really appreciate.

Koo

Last edited by Koo Schadler; 08-08-17 at 01:25 PM.
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Old 10-08-17, 02:10 PM
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Koo Schadler Koo Schadler is offline
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Hi All,

George sent the following replies...

1. Is the concern of cracking due solely to the high solid content in the Tempera Ground, or also a consideration of the binder?

"The high pigment volume concentration of Rublev Tempera Ground makes it less suitable for flexible supports and more likely to crack on these types of supports. However, Rublev Tempera Ground is much more flexible than a traditional chalk or gesso ground. The polymeric binder is very flexible similar to the flexibility of acrylic polymers."


2. Why is backing a flexible support with a solid support (paper on wood panel) potentially not enough to prevent cracking?

"A rigid support decreases the exposure of hygroscopic materials (paper) and hence reduces the degree to which these materials expand and contract due to changes in relative humidity, but does not prevent the paper from expanding and contract."


3. Any reason(s) to coat paper with either the Fluid Medium or GAC 100 when using NP's Tempera Ground as a base for metalpoint drawing?

"This is not necessary when using Rublev Tempera Ground."


4. I'm thinning Tempera Ground with water when building up multi-colored layers for a drawing because I want to apply the thinnest possible layer. The Natural Pigment's website says don't thin more than 20% with water, further dilution can be achieved with the Fluid Medium. What are the consequences of adding too great a percentage of water to the ground - underbound, cracks, flaking?

"The consequences may be underbound ground, depending upon the absorbency of the substrate."


5. At some point does the ground cure and is no longer water soluble (and thus not dissolved by wet sanding)?

"The polymeric binder in Rublev Tempera Ground is not water soluble once it has dried and will not redissolve by wet sanding. However, care must be exercised when wet sanding to avoid excessive moisture and/or heat as this cause the binder to “gum” up no the sandpaper."
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