Weighing Hydroquinone when mixing Developer

ypkennedy · Jun 23, 2018

When mixing a developer that uses hydroquinone I have noticed that after weighing and pouring the HQ into the developer solution there is always some HQ clinging to the sides and bottom of the weighing vessel. So today I weighed that vessel (51.8 grams), added the HQ to the vessel (in this case, 18 grams) then added the HQ to the developer solution. I then reweighed the vessel which contained HQ residue. [See photos. They are stitched together. Proceed from top to bottom.] Sure enough, the weighing vessel now weighed 51.9 grams. So from now on I’ll try to remember to add an extra tenth of a gram of HQ when mixing that particular developer.

Alan9940 · Jun 24, 2018

Hmm, I use disposeable anti-static mixing trays used by labs and I've never had that much residual chemical remaining after dumping it.

drpsilver · Jun 24, 2018

23 June 2018

Ypkennedy:

What you propose is correct. You have two other options: (1) purchase a supply of weighing papers, or (2) purchase a rinse bottle in which to rinse your weighting dish. Both of these should be available at a lab supply store. I would recommend the weighing papers (what I use). The downside of a rinse bottle is that you have to make sure the weighing dish is completely dry before weighing the next compound. If you are making 1 liter of developer, for example, instead of starting with 750 ml, maybe start with 700 ml to allow for rinse water volume.

Hope this is helpful.

Regards,
Darwin

Europan · Jun 24, 2018

I use a simple balance whose brass dishes can be lifted off and I wash them in the bath that I make. All HQ goes into the bath.

mshchem · Jun 24, 2018

drpsilver said:
23 June 2018

Ypkennedy:

What you propose is correct. You have two other options: (1) purchase a supply of weighing papers, or (2) purchase a rinse bottle in which to rinse your weighting dish. Both of these should be available at a lab supply store. I would recommend the weighing papers (what I use). The downside of a rinse bottle is that you have to make sure the weighing dish is completely dry before weighing the next compound. If you are making 1 liter of developer, for example, instead of starting with 750 ml, maybe start with 700 ml to allow for rinse water volume.

Hope this is helpful.

Regards,
Darwin

All excellent advice! Slick magazine paper will do in a pinch for weighing paper as well. When I slaved over a lab bench we had Whatman weighing papers, plastic disposable weigh boats, expensive analytical glass weighing funnels for precise quantitative analysis . I save my wife's little single serving hummus and apple sauce plastic cups. These are as nice as the real thing. As mentioned a wash bottle helps to rinse out the plastic boats.
Mixing your own chemistry is a lot of fun.
Best Regards Mike

Kevin Caulfield · Jun 24, 2018

For weighing out very small amounts, I use the reusable silicone muffin cups. I find them ideal for anything from a tenth of a gram up to about ten grams. Once used they get rinsed in hot water and inverted to dry, ready for the next use.

hadeer · Jun 24, 2018

I am inclined to think that 0.1 gram on a total of 50.8 grams would make no significant or visible difference in the results. It is less than 0.2%. Small differences in developer temperature would presumably have a much bigger effect. So spare yourself the worries.

Patrick Robert James · Jun 24, 2018

I use little dixie cups. Zero the scale after each chemical and residuals won't matter, then rinse the cup into the developer. Toss the cup.

Doremus Scudder · Jun 24, 2018

Just rinse your weighing vessel off into the developer (or swish it around in the developer itself till it's clean). Drain, rinse well and dry. A bit of water shouldn't hurt a stainless steel cup...

Best,

Doremus

craigclu · Jun 24, 2018

Another variable to consider is the scale itself. Mid-range scales tend to have load cells that are less accurate at the extremes of their range. I had an Acculab (different model though) in my darkroom that behaved in that manner but if I included a 50 gram additional load before taring, I could get more repeatable results on small amounts. In my former work, I worked with extreme, vacuum chamber scales and bi-weekly metrology reviews. Even at that level of accuracy if a load cell showed a bit of tendency to behave that way, we would pre-load a bit and the performance would return and defer a $25,000 commitment to a new unit.

Raghu Kuvempunagar · Jun 25, 2018

ypkennedy said:
So from now on I’ll try to remember to add an extra tenth of a gram of HQ when mixing that particular developer.

Not convinced that this will give you the accuracy in weight that you're looking for. What if the next time you weigh HQ, only 0.075g of HQ is clinging to the sides and bottom of the weighing vessel? Rinsing the vessel with water and adding the rinse water to developer is probably a better solution.

Tor-Einar Jarnbjo · Jun 25, 2018

hadeer said:
I am inclined to think that 0.1 gram on a total of 50.8 grams would make no significant or visible difference in the results. It is less than 0.2%. Small differences in developer temperature would presumably have a much bigger effect. So spare yourself the worries.

It worries me a bit that you are the only one here pointing out this obviousness, while so many of the other responders suggest solutions for a non-problem. I am not sure where you get 50.8g from, the amount of developer weighed is only 18g, but the point still stands. The difference is for the purpose of mixing a developer insignificant (about 0.5%) and below the accuracy of the scale used.

@ypkennedy When was the last time you calibrated your scale?

BradS · Jun 25, 2018

hadeer said:
I am inclined to think that 0.1 gram on a total of 50.8 grams would make no significant or visible difference in the results. It is less than 0.2%. Small differences in developer temperature would presumably have a much bigger effect. So spare yourself the worries.

What I was thinking too....but, over the years, I've learned not to even try to dissuade people from their fanaticism. This is up there with putting the loaded camera back into the freezer between usage so as to "preserve" the unfinished film...

Andrew O'Neill · Jun 25, 2018

Can't you just pour in some of the developer back into your weighing vessel, swirl it around, and pour back into developer?? ...but then it's such a teeny tiny amount, you won't notice any difference, so I wouldn't worry about it.

hadeer · Jun 26, 2018

Tor-Einar Jarnbjo said:
It worries me a bit that you are the only one here pointing out this obviousness, while so many of the other responders suggest solutions for a non-problem. I am not sure where you get 50.8g from, the amount of developer weighed is only 18g, but the point still stands. The difference is for the purpose of mixing a developer insignificant (about 0.5%) and below the accuracy of the scale used.

@ypkennedy When was the last time you calibrated your scale?

Thanks for the moral support. I mistakenly took the weigt of the vessel for the weight of the developer, but then again, as you say it is very unprobable that is would make any difference. I often mix developer for a single film with amounts as small as 0.8 gram a shot (borax) but never worried about clinging particles nor saw any unexplainable differences in results. I suppose that variations in developer temperature, movement, shutter/diaphragm inaccuracy, manufacturing tolerances, chemical alterations in your stock solution or even your eyesight have a bigger effect and they might for that matter even cancel each other out.

AgX · Jun 26, 2018

I assume the error of your scale (readout 0.1g) is larger than the weight of the residue.

Weighing Hydroquinone when mixing Developer

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