Migrating graphite

Yes this is a COMMON myth and why we added it to our “Myths, FAQs, and Common Misconceptions” document that can be found in the Resources section. Just like charcoal, particles of graphite can become dislodged during the painting process depending on the size and shape of the particles and can therefore become incorporated into the paint (often less so than charcoal). However, graphite does not migrate through oil paint layers over time. Here is an excerpt from the document I cited above:This has become a common misconception amongst artists that can be easily explained. Most paints containing fatty acids (oils, alkyds, and egg tempera) can become more transparent as they age. The predominant effect is caused by the conversion of higher refractive index pigments (such as lead white, zinc white, etc.) into soaps, stearates, and other complexes that have a lower refractive index, and therefore create a more transparent paint layer that eventually exposes the underlying paint layers or underdrawing. In oil paintings, this is further compounded by a slight increase in refractive index that occurs in oil binders over time. This given the optical impression that an underdrawing (done in graphite, for example) is “migrating” to the surface when in fact it is simply a natural chemical change that has occurred in the overlying paint layers. This phenomenon is also associated with the term “pentimenti,” as the increased transparency of the uppermost paint layers can reveal earlier compositional changes and even unrelated paintings or sketches.