In article , Stuart Noble wrote:
A lot depends how sloppy the mortar is. Mortar dyes are dispersions of
oxide particles so they shouldn't wash out, any more than the sand does.

That would make them "pigments", not "dyes" in most uses. For
practical purposes, that equates to "inorganic and insoluble" not "organic
and soluble".
Brown pigment required, reasonably stable on a million-year
sun-&-rain basis of testing? I'd look at variations on burnt umber,
limonite and the like. Do plenty of batch testing, and specify in great
detail to the supplier that you want a hydrous iron oxide and nothing
else. Ask them for the chemical analysis - should be around about 60~70%
(by weight) iron.
Only thing I'd be a little cautions about is that I'm not sure of
how umber would react to the high alkalinity of a lime mix. Like I said,
batch test.

--
Aidan
Aberdeen, Scotland
Written at Sun, 03 Dec 2006 13:43 GMT, but posted later.