1st Various Helmets.
Burgonet, fish-crest Helm & Gladiator "Murmillo" Helm
- These could be inspirations for Ulmo's Wave-Crested Helm and
other Ainur-Helmet Designs. I also see simiolarities to the númenórean "Karme" Helmet.
Maybe also the Falmari and Falathrim designs were inspired by Fish-crest designs?
2nd: Masked Helmet Types. Various Viking, Roman & Asian Designs.On the Right Medieval Full-helmets, Hounskull, Fuchshelm, Jousting Helm & Armet Designs.
-We know the Dwarves wore masked Helmets, some of their Masks could be inspired be these historical Designs. Also some of the Guards of Gondolin wore Eagle-beaked masked-helmet. I wonder if those could have looked similar to a Hounskull or Armet. The Wich-King wore a Mask too, so masked-helmets could also be an option for the Dark Side.
3rd. Broad rimmed Helmets. Carolingian, Kettle Hat, Sarmatian, Gold-Hat, Capeline, Iron Hat, Roman Cassis, Pappenheimer, Japanese Kawagasa Type Helmet.
-We know that the Orcs wore Helmets with a broad rim, but also some of the Helmets in Smaug's Hoard looked like such types, they may have been dwarvish or northron designs.
4th. Winged Helmet Designs. POhrygian, Assyrian, far E$astern & Bronze Age designs.
-We know the Guards of Minas Tirith wore Winged Helmets, but also some Warriors of Gondolin. So Winged Helmets should be an Option for some of the Noldor and maybe later the Edain.
5th. "Tall Helmet", "High Helmet". Various Designs, Iranian, Sarmatian, Gold Hat, Spangenhelm, Asian, Sogdian & Bronze Age Designs.
-Helmets are often described as "Tall or High Helmets" in Tolkien. The Mouth of Sauron wore a High Helmet, both Elves and Numenorean wore High helmet types too.
6th. Spiked Helmet. Iranian, Sarmatian, Pickelhaube & Bronze Age Type.
-Most famous Ecthelion wore a spiked Helmet Type. So would be a possibility for Elves and maybe Edain.
7th. Crested & Feathered Helmet. Roman, Illyrian, Greek Hoplite, Phrygian & Assyrian Types.
-Some Feanorian and Gondolindrim Warriors wore Crested Helmets or Helmets with Feathers and Plumes. Should be an option for Noldor and Sindar, maybe Edain too.
Some Tolkienian Helmets,
Winged Helm, possibly Elven or Edain
posasible Crested and Plumed Variants.
Conical or Pointed Helmet or Cap or "Jelly Bean".
Númenorean Crown Of Gondor and Karma Helmets. Possible designs for Winged and fish-crest helmet types.
Dwarven: Jellybean caps or Hoods or Conical or pointed Helmets. Some maybe Spangenhelm variant, some similar to Iron Hat and Gold Hat designs.
Orcish: Not much detail. possibly brimmed Helmet and simple pointed helm or ironcap designs?