Quote Originally Posted by MacMillan of Rathdown View Post
About half way up the kilt on the R/H side of the apron is either a kilt pin or a small buckle to keep the apron in place.
I suspect it is a kilt pin of some sort, much like the one worn in this painting by Kenneth MacLeay of Farquhar MacDonald (left) & Lachlan MacDonald (right).



Note the one on Farquhar MacDonald's kilt that looks very much like a Penannular brooch. Though Brown's is partially obscured, it closely resembles the one worn by MacDonald above.
Having collected a number of MacLeay's prints I note an absence on many of his subjects of wearing any sort of kilt pin, with the exception of Brown, MacDonald & William MacDonald (below):



the Prince of Wale's Piper, shown with a banner embroidered with the arms of the Prince of Wales, and in the background is Abergeldie Castle. Note the kilt pin about midway down, under the dirk.
Also note how much higher the kilt pin was worn (when worn) during Victorian times by these individuals.

I love MacLeay's works of "Queen Victoria's Highlanders"