MITRA Forum Question Details

PVA is often recommended as a size for canvas substrates which are composed of cellulose just like paper. I personally prefer acrylic mediums over PVA as a size for oil paintings but PVA is a perfectly suitable material for this purpose.

I generally recommend the application of a ground rather than just painting on the sized substrate. My reasoning for this is that it masks and yellowing of the fabric. The yellowing can through a work out of balance. Many artists did this anyway and if that is the aesthetic you are interested in, the technique is sound in principle, One would just need to make sure that there is enough size to prevent the absorption of oil from the oil paint.

​I would not recommend layering PVA or acrylic over casein as an isolation coat for work in oils. The water from the sizing will likely swell the paint beneath and at best the result will be a crazed glue layer. 

I do believe that oil over a PVA sealed drawing is probably fine, especially if adhered to a rigid support. This would not be my idea of “best practice” but it would be fine (as long as the paper was sized to the proper degree, neither too little causing over absorption, nor too much compromising adhesion of the oil layers). I would want the paper adhered to the panel before application of the PVA to ensure planarity. If one wanted to apply the PVA before adhering to a rigid substrate, I would stretch the paper before drawing and sizing.

A drop of oil may be a good indicator, but I would suggest that oil paint thinned with solvent would be a better choice.

I agree that PVA would be a poor choice to isolate casein. Also, casein is very brittle in thick layers, I would suggest adhering the paper to a panel before and thickly applied casein paint. I know that is was historically used on paper but thick applications of casein and gouache on lighter weight papers can easily crack and this could be an issue when attempting to adhere a previously painted casein on paper after the fact.