MITRA Forum Question Details

​Hi - We do not know what is in the Zecchi product and would encourage you to communique with them directly to understand what their thoughts are about the suitability of their paints for buon fresco. I can say that in general acrylic binders are quite resistant to alkaline surfaces and materials. In fact acrylics are often included in plaster recipes to increase chip resistance - such as our own Acrylic Modifier for Plaster. But it is also important to know that the acrylic binder does not on its own protect pigments that might be alkaline sensitive - so pigment selection remains critical.

On that front, traditionally all organic pigments, including synthetic ones, would be avoided. However we are also unaware of any rigorous testing that directly shows if this is true for all organics, without exception - including the Quinacridones, which are often listed as alkaline resistant by the manufacturers. The real question might be just how resistant are they, since fresh lime plaster would an extreme case. In this regard, the RealWorldColor is interesting since the author's own testing appears to show the Quinacridones as stable for fresco. If wanting to be more adventuresome, and willing to do additional testing on your end, you can certainly evaluate the palette given here:

http://realcolorwheel.com/fresco3colorchart.htm

Just keep in mind this comes with no guarantees that your own experience would be the same, so do as many trials as you can.

Obviously the safest method is to stick mainly with a truly traditional, well-proven list of colors, such as this one:

http://www.noteaccess.com/MATERIALS/FPigments.htm

This can be safely supplemented with any other iron oxide pigments.

Hope that helps.

If I understand the question correctly, it seems to me that secco painting, as compared to buon fresco, is always applied on a wall that has dried and preferably cured. Therefore, the pH sensitivity of the pigments is less critical than with true fresco (where they are applied into a wet wall of calcium hydroxide which converts to calcium carbonate in the presence of carbon dioxide). Secco paints only need to withstand the pH of their binder and any residual pH of the carbonated lime. The wall would be chemically the same as limestone. As to the suitability of acrylic, it would seem fine. The only issue could be if the acrylic component is high enough this could result in a pronounce sheen. This is really true of almost all secco techniques as compared to buon fresco. Casein and distemper are probably the best in terms of this issue. The continued solubility of animal glue makes distemper a poor substitute in terms of longevity.

Apologies if I misunderstood your question.

I also have no experience with the Zecchi product or its formulation so I can't comment about it efficacy.