The Royal Écossais Tartan
Since the historical sources do not give a clear answer, it is just an educated guess that the grenadiers of the Royal Écossais wore the personal tartan of Lord John Drummond (1714 - 1747), but it seems quite obvious.
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The Royal Écossais tartan is a reconstruction variant of the personal tartan of Lord John Drummond, Colonel of the Regiment Royal Écossais (1744 - 1763), shown in a painting which was painted by the Italian court painter Domenico Duprà in 1739. The portrait of Lord John Drummond, which is in the National Galleries of Scotland, served as the inspiration for  R.L. Heil of Eighteenth Century Tartans who reconstructed the Lord John Drummond tartan in 2013.
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We, the members of the La compagnie des grenadiers du régiment Royal Écossais re-enactment group, proudly adopted the tartan of Lord John Drummond as the regimental tartan for the portrayal of the grenadiers of the Regiment Royal Écossais.

 

 

 

 

Photo credit: R.L. Heil, Eighteenth Century Tartans
Photo credit: R.L. Heil, Eighteenth Century Tartans
 Photo credit: Christian Kretzschmar, Bildgabe ©2014
Photo credit: Christian Kretzschmar, Bildgabe ©2014

R.L. Heil wearing Royal Écossais tartan

Reconstruction by Eighteenth Century Tartans (2013)

 

 

Herringbone selvedge reconstruction
Herringbone selvedge reconstruction

Herringbone selvedge
Mid-18th century style