Question about Black Sabbath instrumental

On the album ‘Master of Reality’, there is a short, eerie instrumental just before ‘Children of the Grave’ called ‘Embryo’. It sounds like it’s played on a bowed instrument, maybe a cello.

Any idea who wrote/played it? I always presumed it wasn’t a member of the band. There are no credits on the album for it, IIRC, and I think they did credit Rick Wakeman for playing keyboards on ‘Sabra Cadabra’ (on ‘Sabbath Bloody Sabbath’).

Tony Iommi wrote and played it. It does sound like there’s a cello or double bass playing the low line, but I believe this effect is a combination of Iommi’s very slack tuning (down a minor third) and hybrid picking (using both a flatpick and his fingers to play the two parts).

Thanks Biffy. Do you know if it’s in standard tuning?

The tuning is C#- F# - B - E - G# - C#.