Sorry it's taken so long to get back to this.
keifer113; The only Greek helmet types I know of are from popular media (TV & Films) and a few descriptions in books, and they only present the 'classic' helmet with the front-to-back crest.
And if I've never come across the Spartan officer one, how can I reference it?
'Roman' Crests.
This one has the plasticard spine in common with the 'Greek' crest. But the bases of the brush is made from horizontal layers instead of the vertical layers of the 'Greek' pattern.
You'll need to get your hands on some plasticard tubing for this one, available from Model-railway/road shops. You can use different dameters for the layers, but the base layer must have a similar curve, if not larger, to the helmet you're using.
You will also need a piece of plasticard for the spine of the brush, and if you want to mount it above the helmet, a plastic rod though a rounded piece of sprue might do.
I'll describe this scratchbuild using just one diameter of tube.
Cut a ring of the end of the tube about 3mm in depth which will become the width of the crest.
You'll need to cut this ring into three pieces, a long and shorter pieces. The long should be the length of the arc you want the crest, this will mean using the helmet it will attach to as guide.
I cut this piece to approximately 12mm in length, but it's hard to measure because of the curve.
The two shorter pieces need to be slightly about 0.5-1mm smaller in length and width than the longer piece. You can shorten them at this point or wait until they're stuck together.
In the centre of both drill a hole for the plastic rod you will use to raise it above the helmet.
In one make a cut in the middle lengthways for most of the length. It's best to use a sawbladed craft knife an not cut it in half. This cut will form a slot for the spine to fit in.
Glue them together with the slot on top and the holes lined up. If you're using the same diameter of tube for both pieces they will want to deform from the arc.
Once set you'll need to files the ends until they form a single edge on each end, and if you haven't reduce the width beforehand, do it at this point. Now you have the base of the crest.
Take the long piece and try it on the base, it should appear to form a lip to the base. Mark out the base where it meets the long piece on that piece.
You will have to cut out an oblong from the centre of the long piece within the marks. This is so that when the long piece is glued to the base it has enough area in contact whilst also forming a trough.
Glue this piece in place once you're satisfied.
Make the spine of the brush in the same manner as the one for the 'Greek' crest, but this time you may have shape it's base to better fit the slot you made, and you will need to remove a square of plastic in the bottom-centre to accommodate the rod.
Glue the spine in place and once set glue the rod in place.
Then use greenstuff to form the brush itself using the techniques I described in making the 'Greek' brush.
This is how I made the one on the first scout below.