What I want from a modifier in my paint medium is usually the addition of a varnish quality, i.e more transparent body and satin or gloss lustre. A modifier like damar, venice turpentine or canada balsam can also even out the appearance of different pigments upon drying, so matt and gloss drying pigments all appear unified. Shadows appear deeper when in a gloss medium, and colors more vibrant.
My choice modifier is Canada Balsam, a resin from Abies balsamea. The balsam is actually akin to a thick version of turps: “Canada balsam oil does not differ materially in composition or properties from ordinary turpentine oil” (http://shop.kremerpigments.com/media/pdf/62110e.pdf)
According to wikipedia it has a “refractive index to that of crown glass”, which is pretty cool 🙂 – I dissolve it in gum turps then dissolve this into sun oil or stand oil (or a mixture of both), the ratio’s change according to needs but that is my basic recipe.
From Natural Pigments: “Unlike rosin and Venice turpentine, there are polymerising monoterpenes and diter- penoids in fir balsams. This means that the varnish film is not formed purely by evaporation of volatile essential oils alone, but by the joining together of components such as β-phellandrene (a monoterpene oil component) and cis-abienol (a solid diterpenoid component). This results in a much tougher and more resilient final varnish film if the resin is used alone to make a varnish”
There is also the point that apparently Canada balsam remains amorphous and does not crystallise, so good stability over time. Its used for making permanent microscope slides. This gives an indication of what an awesome optical quality it has.
As mentioned in an earlier post… I find damar problematic for its lint and atmospheric-pollution attracting properties. I find there are a number of factors around how ‘gummy’ my painting ends up. Of course both damar and canada balsam are crazy sticky when liquid. One interesting difference is you can buy damar in a solid state and redissolve it, but canada balsam is sold bottled in its vicious sap form. But when dry, it has the potential to be as ‘crisp’ and dry as a microscope slide – which it is used for!
Undilute, its extremely sticky, but no gummier than damar when dilute with turps and used in a medium. When dry on the canvas – it is perhaps less gummy. Plus I find my brushes wash easier. Ratio may have some bearing on all that, obviously, and also the quality of the oil faction and the environmental conditions whilst drying.