That's a new one on me - canned lambsquarters. :)

Soaking won't do it so try boiling them in water with 2-3 T of cream of tartar mixed in.

Then there is the ammonia recipe - one teaspoon of household ammonia in each and fill with boiling water. Let sit for 6-8 hours.

Oven cleaner is another possible option.

Dave

Thank you for those ideas. I will first try ethanol, as I recall extracting chlorophyll from leaves in early school using ethanol. I think I do have a tiny jar of cream of tartar at the back of a kitchen shelf, so I could try that. Ammonia will have to wait until it is a bit warmer for working outside.

Have you tried using a denture tablet? I've gotten lots of stubborn stains out with one of these products. My favorite is a loose, granular denture product called StainAway.

I thought about denture cleaners, but did not have a chance to investigate ingredients before finding that the cream of tartar worked.

To save energy, I did not boil the solution, but let the jars soak at room temperature for three days. It did remove the stain.

I will soon reorganize my empties and clean the rest of the lambsquarters jars this way.

Thanks again to Digdirt.