|Suriyothai, queen of Ayutthaya, from the film of the same name|
I made the leather helmets featured in these photos (the one just above taken from this blog: http://martinithai.multiply.com/journal) by using the following steps.
(1) Punch out styrene discs of the right size (1/4" or 5/16", depending) using a punch set.
(2) Give the styrene discs a roundish shape with a jeweler's tool for making round shapes. Drill a 1/32" hole in the center using a pin vise (don't drill the hole before rounding it out as it weakens the disc too much and the disc may crack).
(3) Slice the top half of a figure's head. Drill a 1/32" hole *perpendicularly* down the head using a pin vise.
(4) Glue a length of 1/32" brass rod into the head using crazy glue, keeping the length long (you trim it to size later). Put a small glob of Green Stuff or other putty on the head, apply a little more glue over it and thread the rounded styrene disc (concave-side down) down the brass rod.
(5) To build up the top half of the helmet use either the 1/8" eyelets used for scrapbooking or just apply a small ball of Green Stuff or putty. Mould the putty around the brass rod and contour it with shaping tools such as your wetted fingers, round toothpicks, silicone clay formers and the like.
(6) Once glue/putty is dry snip off the brass rod about 1.5mm from the top of the helmet and quickly sand the tip to shape.
(7) Add leather neck and side flaps with putty. You can also add decorations on the helmet as well as a thin metal ring (if not using the eyelets) at this point.
These eyelets are not exactly the right shape for the helmet tops and only work well with the larger 1/72 figures (not Caesar ones which are close to 1/76). They are somewhat useful though since, if you glue them to the styrene disc (a.k.a. hat brim) with the flanged or widened part facing down, the flange itself resembles the metal ring on the leather hats. Finally, you can fill the open top of the glued-down eyelet with putty and smooth it out while ensuring that the protruding helmet spike remains more or less centered.