Dry wood become dark

[bonsai-max]

Hi, I have a couple of Jin in my ABP and they become black.
This year I gave the plant some iron sulfate, can be a chemical interaction with the Jin liquid ?
I pass over with a brush wood but it's really ard to remove
Any guess ?

 

[Wires_Guy_wires]

Yes, the oozing resin turns black after a while. I'm not sure if it's UV radiation or some kind of fungus or bacteria that convert it to something tar-like.
Time will fix that, but it takes about a year.

Sulfuric acid will stain wood black through oxidation, but it takes a strong concentration to do so and it happens almost immediately (or it will turn into fire). Iron oxide will also turn black. But iron sulphate is usually so diluted that it shouldn't discolor anything.
I would apply lime sulfur again, it should go white in a few days.

 

[Shibui]

Iron definitely stains wood. Not sure about Iron sulfate though? Lime sulfur also degrades over time and jins slowly turn dark. You'll need to apply jin liquid 2-3 times each year to preserve the wood long term and keep the white colour.