WHich Dichromates am I looking for at art chemicals?

[mark]

I am comparing prices on potassium dichromate/ammonium dichromate between photo formulary and art chemicals, to start carbon printing. Photo formulary is easy they have one of each. Art chemicals not easy becasue they have like several pages of each. If I was going to compare apples to apples what do I look at?

[anikin]

For carbon printing you are better off getting DAS sensitizer. Holmburgers is organizing a purchase right now.
Hopefully, you are not too late: http://www.apug.org/forums/forum379/...ml#post1447181

It is much more environmentally friendly and way better than dichromate since you can make your tissues ahead of time and have them ready for exposure at any time - unlike dichromate, DAS sensitized tissue does not deteriorate in storage.

Eugene.

[Vaughn]

Both (dichromates and DAS) have their issues. I believe the clearing bath for DAS is more toxic than that of the dichromates.

But as far as the dichromates, either will do, but I use the Ammonium dichromate(AD) -- which is stronger acting gram-to-gram compared to Potassium dichromate(PD). That is because Ammonium is lighter than Potassium...thus at the same weight of the two compounds, one gets more dichromate using, let's say, one gram of AD than one gram of PD. But once corrected for the difference, they act pretty much t he same.

Vaughn

[mark]

My goal is to do everything with water no special clearing bath, so to begin with I am going with the dichromate. the DAS idea means more chemicals to order and takes the simple out. So is it the reagent version, the purified version, or the GR ACS version of Ammonium Dichromate.

[jorj]

Whichever's cheapest.

[Vaughn]

Whichever's cheapest.

I'll go along with this. One would probably see no difference between the lowest and highest grades. Consistancy would be more important (using the same type/source).

If one is using the double transfer method, no clearing bath is needed. With the single transfer method, a clearing bath is recommended as some dichromate can be trapped between the gelatin and the final support during transfer. I use Potassium alum right after the cooling bath (after the transfer). It has been found that any dichromate left behind slowly hardens the gelatin and increases its brittleness over a lot of time (your descendents will have to deal with it -- not you. But no problem, really, if one keeps the prints flat.

Vaughn.

[CMB]

I believe the clearing bath for DAS is more toxic than that of the dichromates.

Vaughn

To be clear, do you mean more toxic than dichromates or more toxic than dichromate clearing baths?

Charles

[anikin]

To be clear, do you mean more toxic than dichromates or more toxic than dichromate clearing baths?

Charles

I suspect Vaughn meant clearing bath. Pretty much anything is more toxic than warm water

The mix of table salt, sodium sulfite and a bit of potassium permanganate (typically used as drinking water disinfectant) is not terribly toxic, but it's still more chemicals than plain water
But it is more stuff to buy than just the dichromate, so OP's point makes sense.

[mark]

Hold the phone. I have not read or watched anything that mentions a clearing bath for dichromates, and I have been reading a lot. I missed the DAS buy anyway.

[Vaughn]

From the potassium permanganate msds:

The estimated lethal human dose by ingestion is 10 grams, with death being delayed by up to one month: Oral, rat: LD50 = 1090 mg/kg. Oral, human: LDLo = 143 mg/kg.
Epidemiology: The U.S. EPA stated that epidemiological studies of inorganic manganese compounds in humans indicate effects on the respiratory system at levels below 1 mg/m3.
Reproductive Effects: Men exposed to manganese dusts showed a decrease in fertility.
Neurotoxicity: Manganese is neurotoxic.

Just don't eat more than 9 grams, and also your wife can go off the pill...

Potassium alum -- used in pickleing/canning foods, in deorderants -- but this is not to say that all the chemicals we put in our foods or under our arms are actually safe.

To be clear, do you mean more toxic than dichromates or more toxic than dichromate clearing baths?

Charles

The latter.

Mark -- Most carbon printers of old used the double transfer method -- to get the image back to its original orientation (and hide any relief). Since in double transfer exposes both sides of the tissue to water, just about all the dichromate is washed off...thus you may not read much about clearing needs in the older literature.

Another way to clear single transfer is using sodium or potassium metabisulfite. But because this greatly softens the gelatin, it can cause frilling and bubbling of the image. It is recommended that one allows the print to dry for a day or two, which hardens the gelatin -- then clear it in the metabisulfite. I use the Potassium alum right after the cooling bath, followed by the wash. Fits better into my work-flow.