This webpage has a spectacular conversation with explanations on several types of armour, in chronological order. Definitely worth a look when trying to decide what time period to go for.
http://www.dagorhir.com/forums/index.php?topic=26822.0
This image is displayed on the Dagonhir website, though I cannot see the name of the manuscript it comes from. Anybody know the full reference for this?http://en.wikipedia.org/wiki/Kasten-brust_armour
Yes, I know it is Wikipedia but it has a picture that shows the grand-bascinet helmet style beautifully.
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Altar of Saint Leonard churge in Basele by Conrad Witz,1435