The boric acid melts and coats the blade with boron glass. That is all that is happening to prevent scale.
The iron wire binding around the blade was an old way of getting more even heating with a primitive or makeshift forge. Most any knife forge doesn't need the wire wrap.
Also, a properly tuned forge with a neutral to slightly reducing atmosphere won't severely scale up the blade.
Beware that the boric acid on the forge floor will slowly eat away the lining. You have to put in a flux resistant floor or kiln shelving which can be replaced.
A proper anti-scale compound like Brownell's, ATP-64,1 or Turco II is a better choice. Turco II is probably the best anti-scale, but costs near $100 a quart now.
Mixing some satanite into a melted milkshake consistency and coating the blade is just about the simplest reliable method of doing anti-scale on a budget.
I am told pottery slip or a clay slurry works just as well.
Folks are also experimenting with Blaster Extreme graphite spray as an anti-scale with good results.
My "HT Paint" mix is a homemade blend to imitate Turco II. It makes a pretty good anti-scale/decarb shield for HTing blades in a forge. I haven't done it yet but adding some powdered graphite or powdered charcoal may improve it.
This recipe isn't as critical as baking a cake, and I adjust the ingredient ratio a bit every time I mix a new batch. Most of the times, I up the ochre or satanite to get the thickness I like.
10-oz boric acid (roach powder is fine)
6oz borax (20 mule team is fine)
6oz satanite (our old refractory friend)
8oz yellow ochre/ocher (any color ocher should work)
6oz gum tragacanth (I use dry powder, but an 8oz. bottle of leather edge dressing will do in a pinch, just eliminate most of the water below)
16oz denatured alcohol (the cheap paint store variety, not the expensive drug store stuff)
water
Mix the first five ingredients and, add the alcohol until it becomes a well-mixed thick paste (you may not need all 16oz). Add water until it becomes a medium-thick slurry (It needs some water to allow proper hydration and solution of some ingredients).
Try it on a piece of clean scrap steel to check bonding results, and adjust the ingredients as needed. More satanite increases bonding. More alcohol if it is still too thick.
Keep in a tightly capped container, away from heat. A tall wide moth screw top plastic jar is a good storage and coating container. A screw top bed urinal is perfect
Shake well each use, and paint it on the blade with a small brush, or dip the blade and let the excess run back into the container.
The blade should be sanded, cleaned, and have no oils on it. Coat the blade with a nice layer of your "ochre HT paint".
A batch should last for a long time. Add some alcohol if it gets too thick or dry. Add more ocher or satanite to make it thicker.
Let the coated blade dry before HT. You can hold it near the dragon's breath to speed up drying, but slower is better.
Do not use above 1600F as the borates will become corrosive.
I buy the ocher, boric acid, and gum tragacanth on Amazon/eBay. I buy the ProCraft 8oz bottles of ochre, a 1-pound jar of 99.9% anhydrous boric acid, and a 6oz. bottle of tragacanth. Everything else is in the shop already.
