A cementation furnace tended over time can produce blistersteel.
Put Blister Coffin into the furnace. Light the furnace and keep it lit for 7 days. Remove the finished coffin and leave it to cool on the ground for approximately 12 hours during coldsnap and 1 day during everbloom and you will get either 4 Blistersteel Bars or 4 Dross. Blistersteel positive results do not depend on the fuel being full or not. You have 4 hours after the progress bar is filled to remove them or you will receive dross.
Takes 30 branches to fully fuel the Cementation Furnace, each branch adding 3 to the fuel meter.
Blister coffins take 100 real life minutes per every 1% progress.