The patina on it caught my eye. I would give a silver dollar that it’s horse. But who knows. Definitely not goat. Lovely russet. More russet in person. Sort of red Toned brown.
Maybe... mine are fine...leather and stitching are very strong...never treated, still good for “almost daily use” ... ( I carry them arround when visiting militaria shows or flee markets ).Every navigator's briefcase I ever got had red rot, and the gussets tore like soggy paper.
I'm sure they were never meant to outlast "the duration."
To be honest the patina on the front flap is largely wood stain and abrasion with steel wool to match the original part of the bag, as the front flap is a replacement in otherwise new natural veg tanned leather. The patina on the shoulder strap is wear tear and horse sweat as I made it from an old stirrup strap but the patina on the rest of the bag is original as you can see here-Love the patina on bottom left satchel.
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My collection - top left a vintage Billingham camera bag, top right a vintage veg tanned ‘Cambridge style’ satchel, bottom left and pride of the collection a USPS satchel, bought cheap as a project from eBay. I had to replace the front flap, the shoulder strap fastening strap and buckle and impress the lettering. On the bottom right my Barbour leather Tarras