apples to apples Javel to Chlorox
OK, now, to compare apples to apples (thank you, Alberto!)
calcium hypochlorite: either 70% or 35% available chlorine
sodium hypochlorite: 60% available chlorine
I cannot be sure which form of hypochlorite the recipe used--he called it "bleaching powder".
So using the formula from 1943, below, is equivalent to using a 0.36% solution (sodium) or a 0.42%/0.21% (calcium) which would equate to mixing about as much as 70ml to as low as 40ml of Chlorox in a liter of water. John uses 1 oz (30ml) Chlorox to 36 oz(1080ml) water for his Javel which equates to about a 0.14% solution. Marek uses 20ml Chlorox/liter which equates to a 0.1%. So the 1943 formula is stronger than John's and Mareks but NOT using straight bleach (phew).
6 min full sun exposure, but again, this was with GELATIN not gum. That is a pretty long exposure! Those of you who carbon print, what is a typical gelatin exposure in the sun?? A 6mn full sun gum exposure would certainly be long.
And one little itty bitty question: this was all done before the digital negative era, so would have been really useful when printing film negatives. Does being able to curve a negative nowadays so easily, antiquate the use of Javel? In other words, If Javel does so well to open midtones as shown in Marek's comparison, couldn't one just open up the midtones by curve adjusting today?
BTW In the article:
Eau de Javel is listed as 5% but I don't know with the Arvel papers what the dilution used was--maybe John has that info.
Now I feel better that this is all tidied up in my mind.
For what it is worth--eau de Javel (one "l" is the correct spelling so the
Christina Z. Andersonarticle says) is said to be 4 g. sodium carbonate and 3 g. sodium hypochlorite mixed each separately with a bit of water and then combined in a total water amount of 500ml. This was used to develop "direct carbon" prints or paper such as Fresson, Arvel, Artigue, also a couple "direct carbon" papers from Germany (Hochheimer-Gummidruckpapier and Buhler's direct carbon paper). These are prints made with gelatin, not gum. This is with a 6 min sun exposure in summer, a 2-3% pot bi sensitizer. Eau was put in a tray and print face down in it.This comes from a 1943 article in the BJP. I am going back through about 200 sources I have on gum and this doesn't apply to me per se but thought someone might have use for it before I toss it.
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