All in the (Robertson) Family (the tartan, not the TV comedy)

[figheadair]

the whole idea of "clan tartans" was devised by the mills as a way to sell more cloth (no, you all have to be dressed in this pattern, which just happens to be for sale over here) (it worked)

No quite. The concept of clan tartans was introduced by the Highland Society of London in 1815 as part of their attempt to preserve elements of Highland culture, including piping and the Gaelic language, that were being lost. The fact that there had never been clan tartans was overlooked in the rusk to 'do something' before it was too late.

It is certainly the case that mills later picked on this but much of it was driven by customer demand.