Birch can be a pain to stain. Ideally you would want to use a spraying stain or toner. Glue sizing and sanding with 320 prior to staining helps. You can also prepare the surface with a very dilute lacquer or shellac instead of glue sizing. Spray the stain or dye. If necessary add dye to your clearcoat and spray to even areas.Thank you all for the input!
I did sand between the first and second coat of poly. I was going to do two more coats with sanding in between. At this point I am going to stop and strip the poly, re-sand, and then stain again. I feel like the mineral spirits may have somehow pulled the stain deeper into the wood after the first coat of poly was put on, though I've never had this happen before. I don't know what other mechanism could be at play...but I also don't know a lot.
Maybe I will wait a full week before putting on the first coat of poly to make sure the stain actually cures. I will give you an update. View attachment 442844