Hard blotches on pine

I'm doing this end grain test panel using some 100-year-old old growth pine from my home renovation that used to be framing, and I applied Varathane oil-based pre-conditioner to the left side, which caused these hard edged blotches to pop out. I sanded this down with 80, 120 then 220 before applying stain.

I didn't treat the middle or right sides and they're not really visible. Anyone know what it might be and how I can avoid it?

Here's a photo of what I'm trying to go for:

https://imgur.com/KYAZHdZ

Posted Jul 30, 2026, 2:15 PM UTC