Emma Ruth Rundle has spent most of her career on the fringes of the metal scene. Besides playing guitar in prog/post-metal band Red Sparowes, the gothic folk of her solo work and Nocturnes and the spacey ambience of Marriages has always had a darkness that can’t totally be called metal, but it doesn’t quite fit outside of it.

Similarly, the thick, tar-throated sludge of Baton Rouge’s Thou has always coated over a tender melodic heart that would escape most listeners, buried as it was beneath layers of molten guitar.

On paper, there’s little in common between the two. But the collaborative album May Our Chambers Be Full proves that the two entities have much more in common than you might think.

While Emma’s name has often come up alongside artists like Chelsea Wolfe or King Woman, her own material has much less overt heaviness to it. At many times, this record does indulge in the very low hanging fruit of pairing her country-tinged voice with huge massive metal riffs—and with great success.

But what’s telling about her contributions as a musician is that her atmospheric guitar tone is recognizable before her voice as “Killing Floor” opens the record. At many times, this feels far more like feel more like Thou backing Emma Ruth Rundle songs than Thou bringing in another singer—especially on tracks like “Magickal Cost” or the nine-minute “The Valley,” the latter of which could fit in any of her solo albums.

Not that Thou relegates themselves to the role of studio musicians. They have their share of big riffs and screamed vocals. On “Monolith,” the clean lead vocals are even provided by their guitarist KC Stafford, whose voice adds another massive layer to the interplay between Rundle and Funck. “Out of Existence” and “Ancestral Recall” alternate between atmospheric, Emma-led verses and riffy, power chorded, screamed choruses.

But whether Thou is lending thickness to Rundle’s trademark tense atmospheres or Emma is giving Thou’s brand of sludgy doom a more overt melodic element, what’s most immediately obvious is just how well these two projects fit together. If there was any discord or incongruity in the writing process, it got worked out before it was put to tape. The line between Emma Ruth Rundle and Thou blurs significantly on this disk, and the result is a wonderful collaboration that I had absolutely no idea I needed.