Richard,

I would heartily recommend James Scarlett's more recent book, The Origins and Development of Military Tartans, which was published in 2003, as a source for the latest thinking about the origins of the Black Watch tartan in particular, and military tartans in general. D. C. Stewart wrote in 1950 and did not have access to much of the evidence and resources that Scarlett did.

The MacRae tartan which Stewart is referring to is this one:


It was published originally in 1893 in Old & Rare Scottish Tartans, by D. C. Stewart's father, D. W. Stewart. In that reference the author claims this tartan to be based on a fragment of a kilt worn at the Battle of Seriffmuir in 1715. I do not know what D. W. Stewart's evidence for this was (Peter, do you?) but it must be remembered that none of us are infallible when it comes to tartan. Consider how incorrectly he depicted the so-called "Culloden tartan" in his book.

Wilsons' version of the MacRae tartan shows a much greater resemblance to the Black Watch design.

This is from a sample dated 1820. If you look, you will see that the version D. W. Stewart gives is effectively half the sett of the Wilson's version. If indeed his tartan is based on a "fragment of a kilt" it could be that he did not have the entire sett available. Or it could be that the MacRae tartan began as a simple design and later was changed to the more complex sett (which indeed is what happened to the Black Watch tartan itself). Of course it is just as possible that the MacRae began life as a variation on the Black Watch and the simpler sett was introduced at a later time as a variant of that, and D. W. had his information wrong.

James Scarlett has this to say in his reference:
Plate No XXVII in Old and Rare Scottish Tartans, subsequently named Hunting MacRae... [is] curtailed from the full Black Watch sett, pivoting on, what would have been in the original, the blue square with doubletracking and the black line centred on the green. In respect to the Black Watch, MacRae has blue and green transposed... Wilsons' made a full-length version of MacRae, with a rose overcheck on the second green and so revealing it to be a transposition of the Seaforth tartan...

If the Black Watch is indeed an end product dating from 1749 or even 1739, D. W. Stewart's MacRae cannot have been worn at Sheriffmuir in 1715, but that is of no great import in the present context. What matters is whether [this tartan is a] further example of [a] government pattern. The historical connection between the Mackenzies and the Macraes and the clever allusion contrived by the tartans suggests that they may well be.