What happened here? (Anyone speak Spanish?)

[MikeG.]

This is chestnut*, at least 400 years old:

This is the finish I applied:

Note it's a clear coat (incoloro= uncoloured). This is what happened:

That looks an awful lot like a tannin reaction to me. Is that possible in 400 year old wood which has spent its entire life outside?

I don't know what the product is that I was using. It was spirit based, and looked just like a varnish to me, but the guy in the shop said it wasn't a varnish. Does anyone know what it is? Although I was deeply disappointed with the colour change, I've come around a bit towards liking it as it helps with the contrast to the bricks. The person that counts, my customer (my daughter), loves it, so I shouldn't be so disappointed I guess.

* The top shelf is (probably) elm, and you can see that it didn't react so much.

 

[AndyT]

You probably already found this

https://www.barpimo.com/products/varnis ... pidecor/en

which mysteriously just says "special alkyd resins and active agents". There's a tech data sheet which doesn't reveal much more.
It does say that the incoloro product is just to renew previously treated wood and should not be used on its own outdoors.

 

[MikeG.]

Yeah, not many clues there!

The test piece in the shop showed it on pine, and it was just like a clear satin varnish. The colour change can only be a chemical reaction.