There are several finds of metal buttons from the 14th century, but no surviving garment with metal buttons, from this period. At least none that I know of.
I have often considered the best way to sew these buttons on to a garment. They have really long ”necks”. Why? Are they sewn directly onto the fabric edge, or are they attached the way people put metal buttons on folk costumes in the 19th century? Besides, the 19th century is way too late a period to look at when making 14th century outfits.
When I made my checkered dress I was shown a picture of metal buttons on a 16th or 17th century coat. I can’t remember where that picture came from.😦
Anyway, I did the same thing on my buttoned dress as was done on the 16th/17th century coat.
About a year ago, I stumbled upon this picture of St. Margaret by Pietro Lorenzetti (1306-1348). She is probably from Italy. Today, the painting can be found at Musée de Tesse, Le Mans, France.
Look at her metal buttons. The inside shows the method for fastening the buttons. To me, it surely looks like they were attached the same way. I think the reason metal buttons have such long necks, is that they must be long enough to pull though the fabric. A shorter neck would be preferrable on buttons placed right on the edge, the way you would place fabric buttons.