MITRA Forum Question Details

 Venice turpentine, when it is unadulterated, is the sap extracted from the Larch tree. Resins that retain their essential oils are called balsam (turpentine is an archaic term for balsam. What we call turpentine was originally called essential oil of or spirits of turpentine). However, most of what is sold as Venice or Venetian turpentine is a mixture of larch balsam and rosin. The lowest grades are simply rosin dissolved in a solvent. Rosin is a very poor material and should be considered an adulterant. There are some suppliers that offer pure larch turpentine.

Even if pure there is really very little to recommend the use of larch balsam as an addition to oil paint. It is really just another soft resin. It yellows and becomes brittle over time. More importantly, it remains sensitive to the solvents if the painting ever needs to be cleaned in the future. As a general rule, oil painters should avoid adding soft resins to their oil paint. Please see our downloadable pdf entitled Myths, FAQs, and Common Misconceptions

 https://www.artcons.udel.edu/mitra/resources

 which covers this subject. If you feel that Venice Turp produces some quality that you find essential (I would still recommend experimenting with other additives like alkyd mediums) please include a list of your paint additives somewhere on the painting (on the stretcher bars, etc) to guide future conservators.