Question: Is it technically possible to make a 'Black' Whitewash?
True Whitewash is a plaster-like substance that has been used to coat stone and wooden walls for cosmetic and waterproofing purposes since the dark ages. It is made from limestone, and as far as I know it resists all manner of dyes. I do NOT mean the paint. Watch this video to understand what I am referring to.
The resulting "blackwash" must serve the same purpose as the original whitewash in that it provides water proofing to as near the same degree as the original whitewash.
Pitch and tar, while being black and capable of waterproofing, are not acceptable solutions as they are not as easily applied as whitewash and have undesirable traits (the smell, the adhesive qualities, etc.)
As black as possible. The best answer will be that one that meets the previous conditions and has the darkest tint.