Crystallised sod. metaborate

I made my first batch of PMK Pyro in September last year. I am about 3/4 way through it but noticed over the weekend that Part B has thrown a sort of crytalline deposit. I don't know how long the solutions should last so disposed of it and made some more with 500ml of filtered tapwater and 150g of sod. metaborate.
When I opened the plastic pot it had been sold in, the crystals had clumped together to form quite large pieces. I thought nothing of it and with the water at about 55 degrees mixed the sloution and put it in my storage cupboard which has a pretty consistent temp of about 65 - 75 degrees.
Today I went to use it and at the bottom of the plastic container were large crystals, like sugar, with some stuck together in larger pieces like ice crystals!!
Where have I gone wrong?

Part B is a saturated solution of sodium metaborate. Cooling it down will cause crystallization. Just heat it up, stir and it should dissolve back.

Uhm. Tap water? The directions specifically recommend distilled water because you are making saturated solution. See:

http://www.jackspcs.com/pmk.htm

anikin said:

Uhm. Tap water? The directions specifically recommend distilled water because you are making saturated solution. See:

http://www.jackspcs.com/pmk.htm

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I know the difference beteween distilled and de-ionised water, but do you think the link actually MEANS to use distilled. So often it seems that de-ionised is fine.
As for the solution being a saturated solution; again I understand the basic meaning of such a solution but should it crystallise out as easily as it appears to have done? It was hardly in a cold store when the ambient was about 65-75.

ColinRH said:

I know the difference beteween distilled and de-ionised water, but do you think the link actually MEANS to use distilled. So often it seems that de-ionised is fine.
As for the solution being a saturated solution; again I understand the basic meaning of such a solution but should it crystallise out as easily as it appears to have done? It was hardly in a cold store when the ambient was about 65-75.

Click to expand...

Well, I'm not a chemist, but when you are making a saturated solution, lowering its temperature even a little bit usually causes crystallization, especially if you have impurities in the water. That's how some of those crystal growing kits work . I suspect that in this case they actually mean to use distilled water. De-ionized should be ok, but I would avoid using filtered water which always contains some ions.

If you are getting crystals droping out, you are super saturating the solution.

I have one of the PF liquid PMK kits I've been pulling from since about 2005.

I store in my basement darkroom where it can get down to 60-64f in the winter and it even got down to the low 50's during the power outages this winter.


I've never seen any crystals in my part b.

Thanks for all your comments - I shall note all the observations and in the first instance use distilled water; then if necessary try cooler storage and finally reduce the ratio, although most recipes I have seen state 300g S.M to 1lt water. Thanks again