Colour of Ferric Oxalate Solution

[rdbkorn]

I'm making a 20% ferric oxalate solution for kallitypes for the first time. I'm starting with 2-3 year old powder that I bought from B&S. I added 40 ml of distilled water to 10 g of FO powder (which was lime green) and had a lime green suspension. Heating for short 10-20 second bursts in the microwave turned the solution into a clear yellowish-brown. Is this the right colour, or have I cooked the heck out of it?

 

[nze]

10- 20 in the microwave can be quite long for 40 ml. mine is more yellow green

 

[Joe Lipka]

Should be fine. FO doesn't dissolve completely until it the water temp is about 170F. Mine is kind of a straw yellow color. The powder form of FO is very stable as long as you keep it dry. Once you put it in solution it does start to change.

 

[deejayNL]

if your powder is still lime green, it's still in good condition (the green form contains more iron than the brown form), maybe it's a good idea to only heat the water, and THEN add the powder??

 

[rdbkorn]

Thanks for the replies everyone. I'm trying it out today - it looks yellow/green now after sitting overnight, no precipitate in the bottle. When I added the silver nitrate to make 10 ml of sensitizer, everything seemed fine and i have a yellow-green coating on the paper.

 

[Dana Sullivan]

Ferric Oxalate definitely changes color with temperature. When heated, it turns a yellowish/brown color, then turns yellow/green as is cools to room temperature. If you heat the crystals in a ceramic pan, they will turn dark brown, and then return to their normal yellow/green state at room temp as well.

 

[wilsonneal]

That's the color in my experience.

Last time I made Ferric Oxalate, I used a 600ml beaker with 25ml water, 6.7g B&S Ferric Ox, about 1g EDTA and a 1000ml water bath at 150 degrees. I swirled the solution around in the bottom of the beaker, submerged in the hot water. Went into solution in about 15 minutes. Easiest time I've ever had with this step.
Neal

 

[rdbkorn]

Dana, Neal - thanks for the additional information. I was able to get a couple of nice kallitype prints this weekend.

Paul

 

[Lukas Werth]

the colour of ferric oxalate depends on the amount of oxalic acid it contains. Without or with very little oxalic acid it is brownish. This is best for kallitypes. For pl/pd, you want oxalic acid inside, because prints clear easier this way, and the more oxalic acid, the greener the colour.
The problem with (over-)heating FO is that some of it may deteriorate, that is change into ferrous oxalate. This is also what may happen if the solution becomes old. The solution for such a solution (couldn't resist;-)): drop some peroxide into it, which will turn any ferrous oxalate back to ferric.

By the way, I usually make my own FO from ferrous by adding oxalic and peroxide (which induces the reaction); this way I get the colour I want without any heating in first-rate quality.

 

[israelalanis]

Hello DeejayNL, I read you talked about brown form of ferric oxalate, I bought brown ferric or ferrous oxalate time ago, but I cant use it, do you know If I can force it to work for Kallitype?, because I didnt and it is just waiting to be used.

Thank you, great day.