Potassium Dichromate - a couple of questions (UK)

[UKJohn]

Hi,

For a number of reasons I have been away from alternative printing for a couple of years and am now in a position to start printing again. However I notice that potassium dichromate (I use it for contrast control in the kalitype process) is not readily available to individuals in the UK and although I have a small amount of chemistry remaining I was wondering whether any one could possible help with a couple of questions I have:

1. Can you substitute sodium dichromate for potassium and if so is it obtainable in the UK?
2. What is the shelf life of 5% potassium dichromate solution? (I have about 80ml made up which is I guess about 3 years old).

I'm guessing this has caused a few problems to other UK alt printers and wonder how this lack of availability of potassium dichromate has been over come?

Thank you

John

 

[davido]

Hi John

Sorry can't help with your first question.
I have been using a 5% solution of potassium dichromate in my sodium citrate developer and was wondering about shelf life myself (as mine is at least 5 years old). I found this information on dpug from Sandy King:

"I agree that ammonium and potassium dichromate solutions last virtually forever. But this is absolutely true only if you mix with distilled water as tap water may contain impurities that will make the solution go bad in a very short time. I store my dichromate solutions in clear glass bottles in the dark and I have never had a solution go bad that was mixed in distilled water."

I'm not sure what is looks like when it's gone bad? Mine has a small white blob floating in it? The solution still seem to work though.

david

 

[mnemosyne]

Hi,

1. Can you substitute sodium dichromate for potassium and if so is it obtainable in the UK?

John

It's the dichromate part that makes both substances highly toxic, carcinogenic, flammable and a mutagen,
so it would surprise me if one substance was outlawed and the other freely obtainable.

 

[Jim Noel]

Try hydrogen peroxide in your sensitizing solution. It works for me. The down side is that it is sold in plastic bottles and releases the extra oxygen atom through osmosis. I solve that by storing in totally full small brown glass bottles.

 

[mr rusty]

If you need some, you will find some suppliers on that well known auction site. Now I know and you know it is totally against the regulations to send this stuff through the post, but.......

 

[Hexavalent]

It's the dichromate part that makes both substances highly toxic, carcinogenic, flammable and a mutagen,
so it would surprise me if one substance was outlawed and the other freely obtainable.

Neither the sodium or potassium salts are flammable. Ammonium dichromate is however flammable and therefore sometime has further availability/shipping issues.

 

[UKJohn]

Hi Jim,

Thanks for the reply. Do you use the hydrogen peroxide undiluted or do you make it up into solutions?

Thanks John

 

[UKJohn]

Hi Davido,

That's really helpful thanks. I do use distilled water so fingers crossed all will be fine with the solutions I have.

John

 

[pdeeh]

try these guys: apcpure.co.uk

https://www.apcpure.com/products.php?product=potassium_dichromate_99_acs

 

[Chris Livsey]

http://www.amazon.co.uk/AC-PRODUCTS-POTASSIUM-DICHROMATE-250G/dp/B004GAWDR8

No connection, seems "regulations" don't apply to everyone.

 

[UKJohn]

Hi Chris,

I had noticed there was some for sale on Amazon but was a little wary about ordering it. Although I have just ordered some from apcpure. Will see if anything arrives.

Thanks

John

 

[Andrew O'Neill]

Try hydrogen peroxide in your sensitizing solution. It works for me. The down side is that it is sold in plastic bottles and releases the extra oxygen atom through osmosis. I solve that by storing in totally full small brown glass bottles.

Jim, could you explain why you would put hydrogen peroxide in the sensitizing solution?

 

[Chris Livsey]

Please keep us updated. I used to weigh it out, in a fume cupboard, for a hologram photographer. I have bought some chemicals from the bay and they have been fine, originating from reputable suppliers with too high a minimum or a tade account clause, sealed and unadulterated.

 

[mnemosyne]

Neither the sodium or potassium salts are flammable. Ammonium dichromate is however flammable and therefore sometime has further availability/shipping issues.

I stand corrected then.

 

[pdeeh]

Although I have just ordered some from apcpure. Will see if anything arrives.

APCpure are a perfectly legitimate supplier, and are equally reliable in my experience. They are a trading arm of Atom Scientific.

I have no connection with them save that I have ordered a number of things from them, and my experience is that they are quick, polite and helpful. Indeed, they list dichromate on their site because I enquired as to whether they could supply it.

They send their goods via a carrier (Royal Mail it seems will not carry goods such as dichromate)

 

[mnemosyne]

http://www.amazon.co.uk/AC-PRODUCTS-POTASSIUM-DICHROMATE-250G/dp/B004GAWDR8

No connection, seems "regulations" don't apply to everyone.

Quote from buyer feedback for this item:

"The Potassium Dichromate was poorly packaged in a padded envelope which was not properly sealed and became separated from its packaging in the post."

Sending a 250g box of potassium dichromate in a padded envelope ... Now I can only hope the container wasn't damaged when the whole package disintegrated and the substance set free to expose some poor ignorant guy with this nasty stuff.

 

[Chris Livsey]

Peroxide will break down over time. That can be reduced by only diluting when required, higher strengths are more stable, and storing at a lower temperature and as said full glass bottles. If you dilute then store use di water as the dilution also adds catalytic metals and dilutes the "preservative" usually a chelating agent.

The dichromate is very stable in aqueous soution almost indefinate if di. Again tap water will introduce substrates it can oxidise but it will not, unless very dilute, "go off" as once reacted it is stable again and strength will not reduce further. In volumertric analysis it in can be bought with a specified strength that does not need confirmation testing.

 

[Chris Livsey]

http://www.amazon.co.uk/gp/product/...&pf_rd_t=3201&pf_rd_p=466496393&pf_rd_i=typ01

Apparently Amazon can also oblige.

just a shame the same can't be said about metaborate

 

[UKJohn]

Just received 100g of potassium dichromate from apcpure. pdeeh thanks for the link.

John

 

[pdeeh]

 

[Chris Livsey]

Just received 100g of potassium dichromate from apcpure. pdeeh thanks for the link.

John

good news, thanks for follow up.