I made a coffee table out of pallet wood. If I had to guess there is at least 3 different kinds of wood here and I don't know for sure which they are.
The white you see is home made chalk paint made from drywall mud and white acrylic paint. It had about 2 coats of paint. To protect and finish I choose polycrylic.
Somehow one of the blocks stained the paint yellow. I saw one other block like this but it was not as defined. It reminds me of painting the walls of a former smokers house where the tar seeps through the paint.
I am still new at finishing and I should have realized that I was applying too much polycrylic as you can see the dripping. While that was bad it did show me something. If you see on the right hand side of the block the yellow colour does not go all the way up the block. There is a drip there that goes from white to yellow. That tells me the finish was not the source of the issue? Perhaps just exacerbated it? Most of the wood pictured has a coat of polycrylic on it and that is not a test coat.
I started looking more for the colour and I found one more block that would have been from the same pallet that had a little yellowing.
Everyone of those blocks you see had pith so it should be a fair amount of heartwood. Also the spots where you see a little bare wood was done on purpose prior to polycrylicing (If that is a verb).
Why did the finish turn yellow in those few places? I think it has something to do with the wood itself.
As an aside I just sanded down the finish and most of the paint in that area. The table was meant to look distressed anyway. Still curious what happened so I can try to prevent it or at least be aware of it.