To get Yama’s blessing for using the furnace in OSRS, you first need to unlock the Yama-related area by talking to the Voice of Yama, then speak to Yama himself and complete the required dialogue chain; one guide specifically says not to leave without signing the contract, because that appears to be the key step that grants access afterward. After that, the same guide says you can pass through the fire barrier and use the related mining/material loop, and another source notes that Yama’s Blessing can be activated for 20 minutes once a week.

What to do

  1. Go to the Yama access area and talk to the Voice of Yama.
  1. Accept the teleport/invitation to Yama’s fight area and speak to Yama directly.
  1. Read or skip the dialogue, then sign the contract before leaving.
  1. Return to the relevant area; the fire barrier should no longer block you.

Furnace use

The info I found does not clearly show a separate “blessing from Yama” requirement specifically for the furnace itself, but it does show that Yama’s Blessing exists as a timed weekly ability, and that the furnace is tied to crafting/smithing use in the usual OSRS sense. If you mean the oath plate furnace interaction, the guide-style result suggests you may need special items or shard requirements for that interface, but it was not fully clear from the source snippet.

Practical note

If you are trying to use the furnace for a Yama-related reward or crafting step, the safest interpretation is: unlock the Yama content, sign the contract, then check the furnace prompt for its exact requirement. The public results I found are a bit inconsistent, so the contract step is the most reliable part.

Source note

The most useful current public result I found was a Yama mining/access guide video and a separate guide snippet mentioning Yama’s Blessing duration.