Sumac varnish/resin?

Varnish, in its botanical form, is a kind of poison sumac tree. The sap is tapped like rubber and used to coat and seal things. Staghorn sumac, Rhus typhina, also has a milky sap which hardens to a clearish wax/resin.

In staff meeting today we discussed pottery a little in its being an alternative to plastic. Paul thought that the glazes in pottery could be a potential source of toxins, and I replied that natural varnishes or shellacs could work, although varnish is derived from the poisonous, allergenic urushiol. Perhaps ordinary sumac could be a source of varnish for pottery or wood projects?

Can we think of any other uses for this sort of substance? Processes for tapping? (Likely similar to rubber…)

Interesting idea! Cool substance for sure, but also slightly frightening, using something that allergenic on stuff that's supposed to come into contact with food...

As for waterproofing unglazed pottery, I heard of a method where you apply conifer resin to the still-warm pottery pieces after firing. The resin melts, wicks into the pottery and seals the pores. I imagine if you burnish the inside of the piece and apply the resin from the outside, whatever you keep in the container might not even taste of pine resin... Haven't got around to trying this yet, but I will eventually.

M Ljin wrote:

Paul thought that the glazes in pottery could be a potential source of toxins

I haven't done pottery for decades, but even back then, people were becoming more aware of the need to identify and document "food safe" glazes.

This fellow compared Milk, starch (corn), lard, and a commercial "food safe" product for sealing, so there are ways to slow down what is absorbed. None of them were perfect, but perfection may not be the goal.



I am *sure* I have read of other methods in the past, but that would take a bunch more research.

However, I have had a bad experience with a piece of pottery I thought was sealed, but it wasn't. It acted like an olla through just the base were I didn't realize it was damaging a table top. Live and learn! However, there's a big difference between leaving water in pottery for hours, vs. drinking a cup of water out of an unglazed cup - that leakage takes time!