Jeemsie Laurenson describes the music played by the Picts at a mill on Fetlar:
And they said, “well, we’ll play a bit tune”. They had a string instrument that they call a porsh. They didn’t call it the fiddle you know, but they could play a tune on a string, a horse hair you know.
I assume the “porsh” is the French word “pochette” for a mini fiddle, rather than the Gaelic word “port” for a tune. The horse hair may be following the idea of the fairies playing on a tiny instrument with a single hair for a string, or it may be a memory of horsehair strings used on the gue. Jeemsie was very interested in the Picts (i.e. the trows or fairies).
Listen at Tobar an Dualchais: this excerpt is from 2:42 to 3:10