Oleo resin mediums

​Your question is a good one as it is easy to be confused with the term “pine resin” when sifting through the technical literature regarding the analysis of Old Master paintings. The reason why it is hard to get a sense of just what is meant by this term is that it is INTENDED to be a general descriptor; often conservation scientists will use this term when they only have a general idea as to what is detected during analysis. First a bit of background on “pine resin”….I will limit my response here to focus on paintings that are well over 100 years old as this is what you appear to be most interested. Each member of the Pinaceae family (pine, larch, and others) possess chemical markers that can in theory be distinguished using methods like gas-chromatography/mass spectrometry. However, the principal markers (the diterpenoid abietic acids) will all eventually undergo oxidation and ultimately this makes it difficult to identify their origin. So time is really against us here if we are ever to find out for sure the original source of these markers….in general all you can really say is that “pine resin” (likely rosin or colophony) was detected but in theory these markers could derive from other Pinaceae sources as well. Secondly and perhaps more importantly is that there is really no way of knowing at which point these pine resin markers became an integral part of the painting’s history. These pine resin markers could indicate that the artist originally added some rosin, colophony, and/or related material to their paints and/or varnish coatings. BUT it is equally possible (and likely) that these markers derive from unoriginal restorations or treatment campaigns. Realize that these materials were traditionally used in varnish coatings, wax-resin lining recipes, and even cleaning formulations in the past. So it is not surprising that we often detect their presence in rather old paintings, particularly ones that have been treated numerous times. So in summary I would say this: our instruments are not quite there in terms of being able to paint a definitive picture regarding what Old Master painters used in their binding media. We can really only say what our instruments detect…the fact that the majority of these paintings have been restored time and time again really complicates our interpretation of the analytical results. We had far more faith in our ability to analyze pictures in this manner some 20-30 years ago but now we know better. That being said we cannot really say that van Eyck and others did NOT use resinous additives. They very well may have….sometimes small additions of resinous components are below the detection limits of our instruments so it is possible that we cannot even identify minute additions. But when we do find these markers it is really impossible to know where they originate from. I do encourage you to continue working and experimenting with these types of resins if you enjoy using them and find that you can accomplish certain effects that are to your liking. I would only ask that you read over our “Mediums and Additives” document in the resources section so that you can take the necessary steps to ensure that your paintings are properly cared for in the future. I hope that somewhat answered your question. Finally, there is a brief outline that describes the origin of various resins and varnishes that can be found on the Kress Technical Art History Websitehere for addition information.