Mike Tsayper

I'm sorry for not specifying my answer enough but there's so little info in the google (i have tortured it for several weeks but with very little success) i thought i won't get any answers if my question was too narrow 

On early plate armor:

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One likely example is the "plate of worked iron" described by Guillaume le Breton and worn by Richard of Poitou (later King Richard I of England) under his hauberk during his joust with William de Barres. There are also a couple of surviving examples of iron plate armour dating back to the Hellenistic period. The most famous is attributed to Philip of Macedon, the father of Alexander the Great. The cuirass was made of wrought iron and trimmed with gold.

http://myarmoury.com/feature_mail.html

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Charlemagne's biographer Notker describes the formidable appearance of Charlemagne and his army at the siege of Pavia (774), in full battle gear:
    That man of iron [was) topped with his iron helmet, his fists in iron gloves, his iron chest and his broad shoulders clad in an iron cuirass. An iron spear raised on high against the sky was gripped in his left hand. In his right he held his still unconquered sword . .. [His thighs) were bound in plates of iron . . . his greaves [lower-leg coverings] too were made of iron. His shield was all iron. His horse itself gleamed iron in color and in mettle. All those who rode before him, those who accompanied him on either flank, those who followed, wore the same armor, and their gear was as close a copy of his own as it is possible to imagine . . . The rays of the sun were reflected by this battleline of iron. This race of men harder than iron did homage to the very hardness of iron.

CATHEDRAL, FORGE, AND WATERWHEEL by Frances & Joseph Gies

During the high medieval times, some "one-piece" helmets were made (e.g. norman helmets, king Wenceslas' helmet) weighing about 2-3 pounds. So making a sizeable plate was not beyond the means of blacksmiths of those days, though most of the early helmets were made of several small plates riveted together (spangenhelm). Romans also were making solid iron helmets during the early imperial period (1-2 centuries A.D.) until they got back to bronze helmets (and iron mail for body protection, back from lorica segmentata).

ThomasPowers, I have scoured through "The Knight and the Blast Furnace" but didn't find what i need. Thanks for the second reference, will look there.

The weight and thickness info i have obtained from several sources. Breastplates were typically 2-4 kg, about 2 mm average thickness, more in the center, less on the edges.

I understand there could be a lot of different factors affecting the price. I don't insist the time to make iron into a sheet was the key factor in the cost of pate armor, i was just guessing if it was so. Now i don't think it was (as it could be done just for 1-2 manhours of unskilled labor). Maybe the forging of the bloom was, though that does not seem likely too..

I've found in "The Knight and the Blast Furnace" the author estimates a 10 kg billet was needed to make a 2.5-4.5 kg plate (so the total time should be increased 2-4x times? or less as the forging melts away and it remains less to hammer). He also writes there's no trace of fold-forging so these large ignots should have been made from a single bloom. But the amount of loss in both phases (bloom to billet, billet to sheet) should depend on the speed of work a lot...

Sorry for that. But Chinese didn't make [full] plate armor so the Europe was implied. They were the first followed by Japanese several centuries later afaik.

If you could provide an estimate how the total work time diminishes with additional strikers it would be great

Thanks

Maybe in China but not in Europe. For Europe there's only one dubious passage about water powered ore crushing by Pliny IIRC

I mean large plates, particularly breastplates. Several kings like Charlemagne and Richard the Lionheart were said to wear iron breastplates, and there's the Philip II's iron armor in one museum in Greece, retrieved from his tomb. These were made before the 13th century when trip hammers began to appear in Europe.

I wonder how long would it take to forge a 2.5 kg billet of iron into a 2 mm thick sheet, with a hand hammer?

Trying to figure out the cost of plate armor before water powered hammers became common..