When my children and I collected the sap from the pine trees, we also ended up with extra bits of bark, bugs and leaves. I didn’t think that this would help in my little project, so I set about purifying the sap.
The simplest way I could find to purify the sap was simply to light it on fire. I did this over a simple, homemade strainer and as the impurities burned out, the resin flowed to the container below. This was easy and fast, but it produced a black glob of resin. This still might have every bit as well worked, but I thought I would be more comfortable if I could make resin that wasn’t so charred in appearance.
Here’s what I did: I tied a good amount of the resin into a loose weave cloth and tied it up. Then, I put this into boiling water and let it boil for the morning (the bag slowly extruded the sap over that time). By noon I had a nice thick layer of resin floating on the top of the water which I collected with a spoon. The results are a nice brown, sticky mass that I am confident will help in my creation of ultramarine blue.