"Walnut" is the word you're looking for...
I got a letter from Audi a few weeks ago saying that carbon cleaning is now covered by warranty up to 120,000 miles. I had my 135i walnut blasted at roughly 18k under warranty as well.
The views and opinions expressed in this post are those of the author and do not necessarily reflect the official policy or position of Bimmerpost.
2014 CC R-Line DSG | 2010 S4 Sold | 2010 BMW 135i Retired | 2006 Lotus Exige Sold