MITRA Forum Question Details

​Without testing specific products this is difficult to answer with confidence.

It does not necessarily follow that acrylic does not have good adhesion to oil paint. Knowing that many oil paintings are painted on acrylic grounds helps us to think otherwise. The key issue as to whether acrylic polymers will adhere well to oil paint is if it wets the substrate well. Many acrylic formulations contain wetting agents because water—if used as the vehicle—does not wet surfaces well. Wetting agents help to overcome poor wetting. Acrylic polymers are known to have good adhesion to many surfaces.

Unfortunately, the term "enamel" does not describe the binder of the pen you mention, so it is difficult to provide an accurate answer.

Information about Pebeo 4Artist "oil-based" Markers is also not very helpful:

"The oil-based paint comprises a solvent base + film-forming substances + pigments. It is formulated with a synthetic mineral oil."

"The 4ARTIST MARKER and Studio XL oil paints are different products. The 4ARTIST MARKER is formulated with a synthetic mineral oil, whereas XL oil paints are formulated with vegetable oils. Therefore, the properties of the binders are not the same."

What the synthetic mineral oil and "film forming substances" are is anyone's guess, so this cannot be recommended without knowing more.

When applying a varnish over these markers one must know the solubility of the "film forming substances" to avoid dissolving the marks made with these pens.

The product literature for Pebeo 4Artist markers indicates that the oil-based medium is completely soluble in mineral spirits even weeks after application, and permanently soluble in a proprietary blending medium they offer. Varnishing guidelines recommend only an "aqueous phase varnish" to avoid re-wetting the dry "paint". For these reasons, I would not consider these pens suitable for signing paintings. Also, the listings for this product line on a major art materials retailer site include the AP seal of the ACMI, and while many very lightfast pigments fall in the "non-toxic" category, pigment content is not disclosed, and I expect some colors might prove fade-prone. 

Honestly, I've never been a fan of signing paintings with a pen anyway. I acknowledge that it can be hard to achieve a good signature with a brush and paint, but that's the best way to make sure it's as durable as the painting itself. And, while I have seen some pen signatures that look good, I've seen others that look a little too much like an autograph, if you know what I mean.