Tartan Tess said:
Last summer, I met a man from Scotland who told me he had some tartan fabric at home from his family that was "Mourning tartan" he didn't know anything else about it.
Last month I was at Elsie's (The art of kilt making book) and asked her about it.
She said it would be MacFarlane black and white tartan.
Funny to see this as I had just finished reading the Wikipedia entry on Tartans and found this:
Mourning tartans, though quite rare, are associated with death and funerals. They are usually designed using combinations of black and white.
The source for this is on the Tartans of Scotland page and the entry there is very brief:
Mourning Tartans

As the name implies these are used in connection with death, and are usually a design using a combination of black and white. As usually found, a few existing tartans are already suited to funerals but where specially created the rules appear to be to replace over checks with white whilst maintaining a black ground.

An example is Stewart Mourning, a late design based upon Royal Stewart but having a black ground and white over check. This design is found only in a very rare collection, Clan Originaux.

This is perhaps the most unnecessary type of tartan ever conceived.