The armet is stamped with the marks of the Missaglia workshop, the leading Milanese armorers in the fifteenth century. Originally, it would have been fitted with a visor.
Marking: The marks MY beneath a crown, and M beneath a split cross without bifurcated ends, signify the Missaglia workshop in Milan while under the direction of Antonio, after the death of Tommaso in 1452.
Boccia, Lionello G. Le Armature di S. Maria della Grazie di Curatatone di Mantova e l'Armatura Lombarda del '400. Milan, 1982. for discussion of Missaglia works, see p. 281 ff and especially marks 19 and 19 p. 283.
Williams, Alan. The Knight and the Blast Furnace: A History of the Metallurgy of Armour in the Middle Ages & the Early Modern Period. History of Warfare, Vol. 12. Leiden: Brill, 2002. Microstructure of MMA piece examined, found to be of variable carbon content.