Potassium Iodide as restrainer?

[Nikola Dulgiarov]

Has anyone ever tried using KI as a restrainer in a developer. I couldn't find much info on the web, besides that it's 10-50 times more powerful than KBr, depending on the developer. I even found a recipe that uses 5ml of 0.001% sol of KI per liter of dev(negative). I think it's a mild solvent of Ag halogens.
Greetings

 

[el wacho]

Hi Nikola,
from my readings, that recipe you refer to ( probably Crawley's Fx-1 ) does not use pot. iodide as a restrainer but primarily as a facilitator of edge effects. this post is one of many that talk about it. there is another post ( google it ) which has great info on Kİ. hope this helps.

 

[Photo Engineer]

Iodide is not an appropriate restrainer for use in developers, nor is it a Silver halide solvent. It is used in some developers to enhance edge effects as said in the post above.

PE

 

[Nikola Dulgiarov]

Iodide is not an appropriate restrainer for use in developers, nor is it a Silver halide solvent. It is used in some developers to enhance edge effects as said in the post above.

PE

Guess I was wrong :confused:
Thanks all

 

[Alan Johnson]

In The Film Developing Cookbook p28 it is noted that potassium iodide as a restrainer has not been thoroughly investigated and that it may prove to be superior to bromide.It is suggested to experiment generally with 1/10 to 1/100 the weight of bromide.
That would be the 1998 edition.

 

[Photo Engineer]

I would tend to disregard their comments Alan.

KI was investigated thoroughly for years and is just too powerful and does too many wrong things. It is also less stable in alkali, turning into iodate ion.

PE

 

[CBG]

Interesting about KI not being a useful restrainer. Does anyone have information on how it enhances edge effects?

 

[Photo Engineer]

Interesting about KI not being a useful restrainer. Does anyone have information on how it enhances edge effects?

There is a rather long thread on this related to Crawley developers. It seems to work best with low iodide emulsions, by adsorbing to the surface and then being released imagewise.

PE

 

[Alan Johnson]

Interesting about KI not being a useful restrainer. Does anyone have information on how it enhances edge effects?

Geoffrey Crawley wrote recently that there is no point in adding iodide (to FX-1) with modern films.I believe this is because they have a lot of iodide in the emulsion. In 1961 Crawley found an edge effect with Adox KB 17,similar to the present Adox/Efke 50 and some other but not all films of that era.He wrote that that the effect probably works by shortening the inductance period,thus "setting" fine surface detail.Also the presence of iodide ion may enfeeble the developing agency and predispose it to produce adjacency effects.To me this suggests that there is more time for developer to diffuse laterally from unexposed to exposed areas,resulting in an increase in density at the edge,though Crawley does not give a detailed explanation.
It is to be expected that since Crawley published (BJP Jan 6 1961) iodide content of some films has changed,nobody ever did any tests to see if there is still an effect of iodide with other films having emulsions unchanged from that era,if there are any.So apart from Adox/Efke 50,assuming it is still the same,there are not really any claims that iodide addition works with any current emulsion.

 

[Photo Engineer]

At the time of that writing, surface iodide ran from zero to 3 mole percent. Today it runs up to 10 mole percent.

The adsorption theory related to the Crawley developers seems to me to be the most logical as then it acts like surface iodide and also acts imagewise. And, it explains why they mostly don't work today or work poorly.

PE

 

[Keith Tapscott.]

There is a rather long thread on this related to Crawley developers. It seems to work best with low iodide emulsions, by adsorbing to the surface and then being released imagewise.

PE

Geoffrey Crawley himself, says that adding potassium-iodide is a complete waste of time with modern films. I read that in a magazine article a few years ago.

 

[Photo Engineer]

Your statement was in the other thread. That observation is well known. I have tried it myself and Bill Troop and I have discussed this topic quite extensively. I believe that Bill has discussed this with Geoffrey Crawley.

PE