MITRA Forum Question Details

From all that I have learned with research on your forum as well as talk with technical experts at both Golden and Gamblin, sizing is an important step to do before applying any ground if oil paint is to be used.

If an oil ground of any kind is being used, the sizing prevents the oil from penetrating the raw fabric. If a chalk or acrylic ground is being used, it prevents any binder seepage from either the front of the canvas (from cracks, fissures, spalls, scraping, sanding, bending, denting, pinholes or uneven application of the ground) or the back (from artist's hands, etc.).

It looks to me, from what you have written, that MITRA recommends PVA as a sizing of equal merit to acrylic dispersion medium such as GAC100 or GAC400. From discussions with Golden, I learned that the GAC products should not be applied to the back of the fabric, because they are hygroscopic, and will rewet with atmospheric moisture, and stick what is below it, after the canvas has been stretched. This was the deal-breaker for me, on three fronts: 1) the sizing was hygroscopic which would lead to greater dimensional fluctuations of the canvas than with a non-hygroscopic sizing like Gamblin's PVA. 2) I wanted to have any dimensional fluctuations that still did occur, happen independently of the cradled panel over which it was placed (stretched). In general building science, two materials that have different coefficient of thermal expansion rates should not be universally attached. Whole surface attachment, like gluing, does not allow relief from minor movements of the two substances, so causes undue stress resulting in things like buckling, spalling and cracking. 3) Indeed, I wanted the paintings on my canvases to be maintainable in the upcoming centuries, so any non-reversible glue – intentional OR unintentional - was not ideal. No glue at all was ideal in this regard.

Other considerations were that the GAC products went on and dried like plastic with greater sheen, and did not penetrate the fabric as much as the PVA. I surmise that the tooth decreases as the shine increases and therefore, I would suspect less adhesion. I also did not like the idea of inability to seal the backside. I suspect that things should either be sealed on all sides or no sides, if air, moisture or temperatures are to spread evenly, without causing instability.

When talking to Dave Bernard at Gamblin, he directed me to size both sides if using PVA so that the fabric fibres were fully saturated, and therefore encapsulated, preventing the possibility of rotting from inadvertent oil seepage as well as destabilizing moisture wicking.

I have done so, scrubbing the sizing in full strength evenly, to every fibre, with a stiff hog bristle short flat brush and scrubbing out any pooling, whatsoever. I do it on a flat surface only. I let the first side dry before sizing the other. This creates no buckling.

Upon discussion with Kristin deGhetaldi, I decided to stretch my fully sized and dry canvas over a fully untreated wooden cradled panel, using the same principle for the cradled wooden panel as for the canvas: full or no sealing. This would prevent warpage of the wood. Any off gassing from the wood to the painting is protected by the sizing. Any off-gassing or chemical penetration from wood sealers is also completely impossible aside from any sizing, because there are none.

Brian, upon these clarifications, how does this sound to you? Thanks so much for you help.

Hi Brian.

Indeed,​ there is evidence that the metal ions in lead can mitrate into adjacent layers of paint and strengthen them. You can find information in the Tumosa - Mecklenburg paper titled "The Influence of Pigments and ion Migration on the Durability of Drying Oil and Alkyd Paints".
I hope this link works ...
https://repository.si.edu/bitstream/handle/10088/20490/12.Mecklenburg.SCMC3.Mecklenburg.Web.pdf

Here is a quote from the abstract:
"But there is now considerable evidence that those metal ions are not only capable of migrating throughout a given paint layer but also sufficiently mobile to migrate from one paint layer to an adjacent one in a painting. In this case the migrating ions are capable of either enhancing or degrading the adjacent paint layers."

In the case of lead, the ions are enhancing.

I am re-reading my post of February 19, 2018, and all the responses below it. As you know, I am hoping to work without toxins throughout my processes. I am seeking to know: can I create a stable painting without them? After laying out my specific questions for you to consider, I will describe my proposed modified approach, based on the answers you have given thus far.

Specific Questions:

Although lead white would add strength to the canvas, will the combination of my various processes create a more than adequate archival stability for my paintings over the centuries?

Specifically,

Can the rigid support (cradled panel) and the alkyd nature of my titanium white compensate for lead white usage in the ground and throughout my painting?

Can a traditional wet imprimatura compensate for the greater absorption of Golden Acrylic Gesso Ground? (I hope so - it seems to do a perfect job of it – performing for the artist during the process just as well as chalk gesso does – with perfect absorption level for the richer glaze layer and excellent surface flow for the subsequent lean paint).

Proposed Process:

1. Size a 16 oz. tightly woven raw canvas one side on the topside while fabric is flat on table. I prefer Gamblin PVA, for reasons already stated in a previous reply.  Snap the fabric when wet to work out any wrinkles. Let dry a day.
2. Evenly stretch canvas over a birch cradled panel, with the weft direction being vertical for maximum long-term support. Use non-rusting strong thumbtacks for easy potential conservation adjustments if ever required.
3. Rewet the stretched canvas after stretching with PVA if there are still any wrinkles to facilitate the pullout of the fabric. Let sit a day.
4. Hand rub and sand five coats of Golden Acrylic Gesso Ground, slightly diluted for smooth application.
5. Allow to cure over several days.
6. With Gamblin Solvent Free Fluid, dilute Gamblin FastMatte Alkyd Safflower Oil Foundation paint (mostly Burnt Sienna) no more than 25%. Rub on a high paint spread imprimatura-priming glaze with a cloth.
7. Into the wet glaze, drop an undiluted foundational layer (grisaille) using Gamblin FastMatte Titanium White and Burnt Sienna and Ultramarine Blue (mixed to the same colour as Burnt Umber). Let dry several days.
8. With virtually undiluted Gamblin FastMatte paints, add another foundational layer (Velatura). Let dry several days.
9. Add several layers, several days apart, each starting with a glaze or scumble of the same paints diluted with no more than 25% Gamblin Solvent Free Fluid, with high paint spread. Then modify the glaze with additions of slightly diluted paint, or in white areas, undiluted paint.  Palette: Gamblin FastMatte Alkyd Safflower Oil Paints:

• Titanium White
• Burnt Sienna (in foundations)
• Quinacridone Red
• Hansa Yellow (in foundations)
• Ultramarine Blue
• Phthalo Blue
• Red Transparent Earth (in glazing applications)Rembrandt Oil Paints

• Transparent Yellow (in glazing applications)

I am looking forward to your answers. Thanks so much for all you do and for your clarifications here.

I am re-reading my post, and all the responses below it. As you know, I am hoping to work without toxins throughout my processes. I am seeking to know: can I create a stable painting without them? After laying out my specific questions for you to consider, I will describe my proposed modified approach, based on the answers you have given thus far.

Specific Questions:

Although lead white would add strength to the canvas, will  the combination of my various processes create a more than adequate archival stability for my paintings over the centuries?

Can the rigid support (cradled panel) compensate for lead white usage in the ground and throughout my painting?

Can a traditional wet premature compensate for the greater absorption of Golden Acrylic Gesso Ground? (It seems to do a perfect job of it – performing during the process exactly like chalk gesso does – with perfect absorption level for the richer glaze layer and excellent surface flow for the subsequent lean paint).

Proposed Process:

1. Size a 16 oz tightly woven raw canvas one side on the top side while fabric is flat on table .I prefer Gamblin PVA, for reasons already stated in a previous reply.  Snap the fabric when wet to work out any wrinkles. Let dry a day.
2. Evenly stretch canvas over a birch cradled panel, with the weft direction being vertical.
3. Rewet the stretched canvas with PVA if there are still any wrinkles to facilitate the pullout of the fabric. Let sit a day.
4. Hand rub and sand five coats of Golden Acrylic Gesso Ground.
5. Allow to cure over several days.
6. With a 25% diluted Gamblin FastMatte Alkyd Safflower Oil Foundation paint, rub on a high paint spread imprimatura-priming glaze with a cloth.
7. Into the wet glaze, drop an undiluted foundational layer (grisaille) using Gamblin FastMatte Titanium White and Burnt Sienna and Ultramarine Blue (mixed to the same colour as Burnt Umber). Let dry several days.
8. With undiluted Gamblin FastMatte paints, add another foundational layer (Velatura). Let dry several days.
9. Add several layers, several days apart, each starting with a roughly 25% diluted glaze or scumble of the same paints, with high paint spread, the glaze subsequently modified with additions of slightly diluted paint, or in white areas, undiluted paint.

I am looking forward to your answers. Thanks so much for your clarifications.

Kathy Marlene Bailey