I was not very happy with the results of this clean today, but it was the best I could manage.
Wool carpet - builders had brought lots of 150 yr old soot down from the loft (lots). The owner had vac'd months ago - so I arrived after it had been down for ages!
The left hand image was after I had attempted to vac it - which made no visible difference. Wool-X and Split-X didn't touch it. I then pre-sprayed with Orange-X, extracted, then pre-sprayed again, extracted twice more. Spot treated with Prochem Pro.
I asked the customer if he'd though about claiming on his insurance - he wasn't insured...

I spent 4.5 hours on this twin staircase!