In recent years, I’ve developed an increasing frustration with materials of permanence. I was doing some work a few summers ago with polymer resin and got frustrated with how over-processed the substance was; how without decomposition it is, how unending. How presumptuous a material.
The thought that sap (or what I later learned is actually coniferous resin) might be an alternative first occurred to me the same summer while staring at a clear amber-like sap deposit running down the side of a tree . It had oxidized to form a translucent casing around the viscous glob. Ironically, the sap from that first tree never worked with this process. I haven’t had success with sap from deciduous trees, and found it to be exclusive to conifers. These trees produce resins and gums, thick secretions that can be heated to create a translucent rosin.
After some internet research, from what I can tell, the practice was largely lost with the introduction of polymer resins, but it’s quite simple.
Spruce gum is scraped off of natural swellings that run down the sides of a tree trunk over wounds that have formed on the tree’s surface. The same method will work for pine rosins that form in smaller, hardened yellow dollops around the tree's trunk, but spruce is more generous with its distribution of rosin over natural scrapes in the tree.
Often, more recent accumulations of spruce gum have a reddish tint and are stickier, making it harder to work with. Older swellings often work better. Once gathered, large debris and pieces of bark can be removed from the clumps.
In an outdoor, well ventilated area, set a burner to low-medium heat. Gradually heat the spruce sap until it forms a thick liquid. (Reminder Spruce gum is a fire starter and is very flammable so don’t touch it to a flame).
Once liquid, add glycerin. For a given amount of spruce gum, add about 1/10 as much vegetable glycerin. Mix in the glycerin until combined. Don’t boil.
When the gum and glycerin have sufficiently combined, the sap can be strained and cast directly into a mold.The result is a water resistant, impermanent resin. It’s brittle, and will get melty in warm enough temperatures.