PMK part B came out of solution

[Loose Gravel]

A couple of months ago I mixed 2 one liter bottles of Part B PMK. I mix this at half strength, i.e. 150 gram balanced alkali to make 1000 ml and then use twice as much as the rest of you PMK folks. It was mixed in distilled water, then set on the shelf for 2 months. I went to use it today and both bottoms had large deposits of crystals within the bottle. One was just on the bottom and the other had it on the sides, too, like condensed water droplets in the shower. Probably 20 to 30 grams worth. It has not been less than 60F in the darkroom, nor above 80F. It is exactly as I have done it before with no residue. I had problems with the 300 grams to make 1000 ml, so I switched 20 years ago. Another odd thing is the crystals are like little BBs. Not a powder. I shook and stirred them, but it doesn't seem to go back into solution.

Anybody seen this before? Should I toss? I did my film today by mixing B part from scratch.

Thanks.

(800)

 

[Gerald Koch]

The solubility of Kodalk is sufficient to make a 30% solution at 20 C. However, if the temperature should go lower then some solid may separate out. Certainly 150 g/l should be OK unless the temperature goes much below 20 C. Did you try heating the solution to get the solid back into solution?

 

[Loose Gravel]

GK

I warmed it a bit, but not hot. I should pour it in a beaker, grind up the crystals, and heat it.

 

[Gerald Koch]

If you are not in a hurry to use the solution just putting it in a warm location for a few days with occasional shaking should work.

 

[Loose Gravel]

I'm not in a hurry. It was just weird. All these years with no problems and then poof.

 

[john_s]

I think that I read somewhere that metaborate should not be heated much to facilitate its dissolving. Sorry I can't remember where.

 

[Gerald Koch]

I think that I read somewhere that metaborate should not be heated much to facilitate its dissolving. Sorry I can't remember where.

Heating sodium metaborate will not cause any problems. Kodak recommends a starting temperature of 50 C when mixing developers that contain this chemical and most others.

 

[gainer]

Heating sodium metaborate will not cause any problems. Kodak recommends a starting temperature of 50 C when mixing developers that contain this chemical and most others.

Perhaps that idea came from the fact that at 53.6 C the molecule doubles in size, including the water of crystallization, becoming 2(sodium metaborate) 8 mol. I used to worry about whether I was getting 4 mol or 8 mol until I found that a certain weight in solution gave the same solution strength whether it went in as 4 or 8 mol.
A possible reason for some precipitation might be the fact that long exposure to air of the dry metaborate allows it to take in CO2 and break down into sodium carbonate and borax. I don't know what the solubilities of these two are in a nearly saturated solution of the metaborate.
I know a little precipitate can often seem like a lot. It may not make a noticable difference.
I have used TEA as the B solution for PMK with pretty good results. IIRC, I used the same amount of TEA that I would have used of the metaborate solution.

 

[highpeak]

I had the same thing happened with my PMK "B" developer, there was some brownish thing at the bottom. I use it a couple of times and I didn't notice any under-development. One roll of film came out a little thin, I think that was because of bad exposure.

Alex W.