variegated rust patina
1.mist on a solution of hydrochloric acid and water allow to dry
(typical mix rate is 1:1 water to the already diluted Muriatic Acid sold for etching cement)
the more solution employed the larger the resultant ferrous chloride residue will be
2.sprinkle (spot)on a solution of technical grade (35%) hydrogen peroxide, water and hydrochloric acid allow to dry
(500ml hydrogen peroxide, 200ml muriatic acid, poured into a 5 gallon container then topped up with water)
3. with a hose handy, flood the steel with a heavy mist of the peroxide mixture you can try various dwell times or mist first with water for a more diluted effect.
4. rinse well allow to dry
step one produces a pickled steel free of rust with deposits of ferrous chloride (iron chloride II) which are loosely attached to the surface, when rinsed of they will rust at a natural rate for oxidation with water
step two produces deep brown spots as with all the rusting, temperature effects the speed and how dark they appear, oxidation occurs from the peroxide
step three is a more general oxidation state from the peroxide
step four washes the ferrous chloride away and is a passivation phase
5. employing the original hydrochloric solution spot\spray the darker areas to burn in lighter specks (i often do this with a light film of water already on the sheet for a more subtle effect)
5A. (optional) repeat steps 2 thru 5 building depth till you ruin it, get sleepy, poison yourself or just give up
6. six passivate the piece throughly with either a pressure washer or as powerful a steam from the hose as you can manage, be careful with a pressure washer as it can create uneven removal (another potential variable you might use to effect)
7. accept the fact that whatever you see while your doing this isnt going to be the end result when you are done, and further that variables beyond you control will impact the end result. Dont expect to be able to easily replicate a finish from one day to the next. temperature, humidity and airflow all effect what you get.
Depending on what I now see I use a propane weedburner for heating, a swamp cooler for higher humidity drying, a compressed air nozzle, different dilution levels, mix levels and dwell times. (have even used straight peroxide)
8. we generally seal with an acrylic (any acid missed in passivation really shows up)
disclaimer
hydrochloric acid will stunt your growth, put hair on you palms and make you sound like a girl (if yoy arent already) review the MSDS and employ all cautions, ferrous chloride will make you a slobbering idiot (if you arent already) its disposal is regulated by the EPA (who will make you a slobbering idiot) and is toxic, review the MSDS take proper precautions and dispose of correctly (note iron chloride II when upgraded with chlorine becomes iron chloride III which is used to etch copper plates, when I find a safe way to do that I'll post it
)