When working with conifers it can get extremely sticky as these trees exude resins from cut stems as well as other organs such as seed cones and needles. We can use our understanding of the chemistry of these resins to work out the best way to dissolve them so we can clean our hands and tools (read on).

Conifer resin helps a tree resist microbial attack, particularly when it is cut, and also acts as a deterrent to herbivory.^ref So you can understand why it might need to stick to the stem and cover a wound. Some of the active components of resin which defend against microbes are volatile organic compounds, or VOCs, which evaporate under normal atmospheric conditions.^ref This wouldn’t be much use to a plant, so the VOCs are dissolved in non-volatile substances, and resin is this combination of both substances.

One study assessed the composition of resin from 13 species of conifers grown in Taiwan and found that the main non-volatile components were ‘diterpenoids’ – these are organic molecules in the terpene family, shown below. You can also see the volatiles they found in this table – α-Pinene was a common one across species.

To work out how to dissolve such a molecule, we need to know what kind of solvent works against it. The rule is ‘like with like’ – you need a similar molecule to dissolve a substance, specifically as it relates to the electrical charge across that molecule – or its polarity.^ref

Water is a great solvent, but only for polar substances – those molecules which have a different electrical charge at one end versus the other.^ref Not only are terpenes including the diterpenoids above not polar^ref, but we already know that water won’t dissolve resin otherwise you wouldn’t be reading this post. For similar reasons soap and water won’t work either, because resin is just too hydrophobic (resisting water).

So we need a non-polar solvent. Unfortunately many of these are nasty substances such as benzene and carbon tetrachloride, which are toxic to varying degrees. They also tend to be produced from crude oil, not exactly a sustainable approach.^ref1,ref2

But another non-polar solvent turns out to be plain old vegetable oil.^ref

This came to me after remembering my year 12 chemistry teacher explaining how soap works. It stuck in my head that soap is able to dissolve oil because the soap molecule has one end which is attracted to water, and another end which is attracted to oil, which it then disrupts so it can be washed away. So if you can dissolve something in oil first, then you should be able to use soap to wash it away.

And this in fact works really well! Put a decent sized drop of cheap vegetable oil on your hands (you don’t need extra virgin olive oil for this one). Rub the oil thoroughly into the resin and over your hands, and you will quickly see it start to dissolve. Step 2 is to add some hand soap, lather well and rinse. One or two rounds of this will remove even the stickiest, blackest, most persistent of conifer resins. And for tools, you can just use the oil and wipe it off versus washing with soap and water, particularly when you have carbon steel which rusts easily.