Here is the earliest known triangular type of flask known in private hands, ca. 1540, the body covered with brown corduan leather, the oberverse fitted with a folded leather pouch that is mostly called a 'ball' pouch. Actually it is much too delicate to ever have been able and hold balls; moreover, their weight would have made the very light flask turn over. I guess that this pouch, at a time when garments were not yet fitted with pockets, was meant to receive the small accouterments badly needed by any arquebusier to clean and maintain his arquebus, such as worms, scourers, wadding, etc.:
Engraved running around the nozzle is an early style of line decoration coresponding to barrels of the 1520's-30's, while the serpent shaped scrolled form of the horizontal cut-off exactly corresponds to the grips of pan covers of matchlock arquebuses of ca. 1525-40:
The spring loaded grip of the nozzle lid represents its earliest form, wrought integrally with the spring which features the wide and characteristically early bow reminding of the springs on sketches by Leonardo da Vinci and Martin Löffelholz, early 16th c.
The edges are reinforced by finley nailed and etremely thin tinned iron fittings. The rounded and embossed washers of the side rings are in exactly the same style as decoration on the forestocks of two North Italian matchlock arquebuses of ca. 1540 in the Vienna colection. The belt hook on the reverse is mounted askew, which also is a very early criterion and does not show up on powder flasks after ca. 1560.
Attached to the rings is the original finely turned dark green cord.
This extremely rare type of earliest triangular flasks is first represented on a painting dated 1529, of the battle of Pavia, 1525:
The only other four surviving examples are preserved in the collection of the former Munich Arsenal, which has been closed to the public for almost twenty years. When I was there I took the photo attached last.