Most people interested in medieval armour think that the word sallet is first attested in the inventory of the Gonzaga family armoury after the death of Francesco I Gonzaga in 1407:
#23: Vna cellata coperta velluto carmesi pilloso cum certis dindinellis racamatis viridis “One sallet covered with plush crimson velvet with certain green embroidered fringes”
#25: Quadraginta tres cellate ferri “43 sallets of iron”
#124: Triginta stufe a celata “30 coverings for sallets”
That is the oldest reference in Claude Blair, and his book in 1958 was the last book on European armour by someone who spent a lot of time reading medieval documents in the original. In fact, there are another group of references from this time which have not yet been brought into the debate. These are in the Archivio Datini di Prato in Tuscany and were published by Luciana Frangioni in her article “Bacinetti e altre difese della testa nella documentazione di un’azienda mercantile, 1366-1410.” She copied and printed all of the references to armour for the head in this archive, and now I have copied them for you.
from 1406 (ADP, n. 178/15, c. 1t)
cappellina d’acciaio celata, buona: s. 18 “celata chaplet of steel: 18 soldi”
celate di ferro, di più fazioni, buone e cattiva, piccole: s. 8 una “celate of iron, of many styles, good and bad, small: s. 8 each”
from 1408 (ADP, n. 178/16, c. 1t)
cappellina d’acciaio celate, verniciate a corna buone, f. 1 una “celata chaplet of steel, varnished, with good horns: 1 florin each”
cappellina d’acciaio, nera, di prova, <<a ghote e choda>>, s. 16 “chaplet of steel, black, of proof, with ghote and tail, s. 16″
celate d’acciaio di Milano, verniciate, buone, guarnite: s. 14 una “celate of steel of Milan, varnished, good, garnished: s. 14 each”
celate d’acciaio di Avignone, verniciate, buone, guarnite di calotta e no: s. 18 una per l’altra “steel celate of Avignon, “varnished, good, garnished with suspension lining and not: s. 18 for either”
celate di ferro, verniciate, cattive, rotte, sfornito: s. 6 una “celate of iron, varnished, bad, broken, unfurnished: s. 6 each”
from 1410 (ADP, n. 178/18, c. 1t)
cappelline di ferro di Avignone, verniciate, per celate, guarnite e sguarnite: s. 14 una per l’altra “chaplets of iron of Avignon, varnished, for celate, garnished and ungarnished: 14 soldi each for either”
In the hundreds of volumes of papers from the 1360s onwards, not one mentions a headpiece called a celata before 1406. It seems that early on, a celata was a kind of cappellina like a brighantina (brigandine) was a kind of little corazza (covered body armour) for thugs (brighanti). The only problem is that I don’t know what distinguished a cappellina from other iron caps!
Now, there is a problem that a shape of headpiece usually appears before it has a special name, and a name for a type of headpiece can appear before it becomes linked to a particular form. Scholars in the last hundred years disagree about what type of bowl celata or Tschaler first referred to. To some, it is a shallow headpiece with the hem flared outwards at the sides and back but fitting close to the skull in front, like the helmet on the right in the photo above. (I say “headpiece” because “helmet” was a technical term at the time when salets were worn: basically, what we call an armet they called a helmet or elmetto). To others, the early sallet is a deep headpiece which slowly lost its separate camail as the sides of the helmet extended over the cheeks and down the neck, like the photo in the upper left. I am used to calling the second type a barbuta, but this is artificial: in 14th century Italy a barbuta seems to have been more or less another word for bascinet, and I suspect that in the late 15th century celata had become the basic word for something iron that you put on your head to stop the nasty people from splattering your brains on the ground. But at the beginning of the 15th century, Italians seem to have had something specific in mind when they said celata.
In the past few years, researchers like Roel Renmans and Augusto Boer Bront have found a few salet-like headpieces in art as early as 1315, but as far as we know the name does not appear before 1406. Datini’s clerks did not describe the shape of these headpieces, although if they had camails, cheek-flaps, or tubes to carry a plume they would probably have mentioned that. Etymologically the name seems connected with celare “to conceal, hide” but when Datini’s clerks described covered headpieces they said coperta in not celata in, and their celate were not covered.
Personally, I think that the price from 1/4 florin (6 soldi) to 1 florin each implies that Datini’s celate were the shallow kind of headpiece, because those are the prices of cheap headpieces and the deep kind would have been difficult to make. There are ten different words for different types of helmets in the published part of Datini’s records, and I don’t understand what more than half of them mean. With continued research, we should be able to nail down just what kind of pot people had in mind when they spoke of a celata in 1406. Very few people interested in medieval and renaissance armour have been looking at documents for the past sixty years, and even fewer have published their work. Italian archivists know of all kinds of things which are rarely discussed in English or German.
Further Reading: Luciana Frangioni, “Bacinetti e altre difese della testa nella documentazione di un’azienda mercantile, 1366-1410,” Archeologia medievale. Cultura materiale Insediamenti Territorio XI (1984) pp. 507-522.