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Stain Becoming Underbound? (And a corollary fat/lean question.)

I read that paint made with OMS could become underbound, meaning that the solvent washes the oil away from the pigment particles and leaves the pigment loose on the surface. Ron Francis said this would feel dry, but pigment would come off if rubbed with a rag because starting with such a wash creates a weaker paint film from the beginning.

Back at the beginning of December, I painted three panels with two coats of Geneva Foundation stain.  Tonight, I lightly rubbed the surface of each with a paper towel, and, sure enough, I saw the familiar brownish neutral there on my paper towel.

Each panel was a "Centurion Deluxe Professional Oil Primed Linen Panel" (medium-textured OP linen adhered to a solid 3mm MDF board).

Is this normal?  (It's possible that I did not apply the foundation as micro-thin as Mark Carder recommends, but these two layers of stain have had two months to dry.)

And this leads me to a second question...  How do I know my Geneva Foundation is fatter than the white OP that Centurion used under my OMS-thinned stain layers?

Comments

  • dencaldencal -
    edited February 1
    I read that paint made with OMS could become underbound, meaning that the solvent washes the oil away from the pigment particles and leaves the pigment loose on the surface. Ron Francis said this would feel dry, but pigment would come off if rubbed with a rag because starting with such a wash creates a weaker paint film from the beginning.

    Back at the beginning of December, I painted three panels with two coats of Geneva Foundation stain.  Tonight, I lightly rubbed the surface of each with a paper towel, and, sure enough, I saw the familiar brownish neutral there on my paper towel.

    Each panel was a "Centurion Deluxe Professional Oil Primed Linen Panel" (medium-textured OP linen adhered to a solid 3mm MDF board).

    Is this normal?  (It's possible that I did not apply the foundation as micro-thin as Mark Carder recommends, but these two layers of stain have had two months to dry.)

    The issue with solvent and unbounded pigment is one of degree. That is to what extent has the solvent diluted the pigment and the binding polymers of the oil ? Will the density of these molecules be sufficient to form a coating when the solvent evaporates.

    A canvas tone/stain has a high proportion of solvent and some loose pigment can be expected on the surface.

    As fatter layers are added on top an intact and durable surface will be created.

    And this leads me to a second question...  How do I know my Geneva Foundation is fatter than the white OP that Centurion used under my OMS-thinned stain layers?

    You don’t know this and there is no way of knowing. An oil primed canvas layer is unlikely to be leaner than an OMS tone/stain layer.  However, it’s likely to have been applied some years ago and factory heat dried. I would suggest that the oil prime coat will be fully polymerised and a stable, hard surface.

    Denis

  • Thanks @dencal.  That's extremely reassuring.  
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