To get the color for those hinges, did you use the Black Dip Pre-Treatment that LCW sells, or was that just the Phosphate?
If you recall, what kind of timing did you use for the hinge vs the spring?
Hinges are supposed to be natural, the springs are darker primarily because of the heat treatment process required.
Timing is difficult to state. In other words, experiment. It is dependent on your water (mine comes from the Sierra Nevada Mountains), the type of phosphoric acid used, the amount of phosphoric acid used, the temperature of the bath, with a 10 minute maximum (self imposed) bath time. There's also a minimum time to achieve a "natural steel" look, about one to two minutes. I'll use a couple of freshly bead blasted bolts as test subjects to determine what my current bath will do.
Hints:
1. Do all your "natural" parts first, the "Black Dip Pre-Treatment" parts last.
2.
Don't do any phosphating if your air temperature is lower than 72F.
3. Air drying seems to be the best method to get rid of rinse water (aka, a dry day). Oven drying tends to leave "flash rust".
When I get finished with all I the phosphating I'm going to do, I pour off the
cooled hot water pan into a 5 gallon plastic bucket and pour in a couple of cups of Borax - an alkali - into the acid bath to neutralize it. Occasionally, I will save the acid bath for use the next day - covered of course. I use Eastwood's metal black (which seems to be discontinued) but pour it into a plastic (Eastwood supplied) container for future use when done. I wind up with the concentrate and my diluted mix. It is not heated to work. I don't know if the stuff you have will function in the same way.
Storage of unused chemicals should take into consideration winter temperature. In Silicon Valley, freezing temperatures are very infrequent (and illegal
).
Jim