Mixing own chemistry

Ian Grant · Feb 13, 2020

I've spent £4,500+ on a set of accurate scales mid 1990's at that point closer to $8,000 than today's exchange rates, maximum weight 1gm to 5 decimal places, and calibrated daily. Even back then we used scales calibrated to +/- 0.5g for less critical work with larger quantities. Because of the nature of our work all our scales had to be independently calibrated.

These days scales for 20-50g +/- 0.01g are really cheap and accurate, the US dealers don't won't to over sell But they are great in the darkroom and can be calibrated.

Ian

Alan Johnson · Feb 13, 2020

These days the old beam scales have rather gone out of fashion but a search for "Lab analytical balances" brings up a selection of today's offerings
The least you are likely to weigh is 0.2 g phenidone and the most 100g sodium sulfite. More than that can be done on a plastic kitchen scale.
The pH may not be necessary but it is often interesting and easily estimated using a roll of 1-14 pH paper. IMO the best quality is reliably made in the US (Hydrion) or Europe, the printed colors actually match the colors of the test strip.

Mainecoonmaniac · Feb 13, 2020

I got a Magna Stir at a surplus store. It helps to dissolve difficult to solids into the solution.

takilmaboxer · Feb 13, 2020

The only thing I ever mix is a quart of D-23. I use a teaspoon and a tablespoon, no scale at all. I own a couple of scales and found them to be unnecessary for such a simple formula. However for more complex recipes I'd go with my triple beam.

AgX · Feb 13, 2020

Rudeofus said:
There are extremely cheap scales to be found on ebay, coming directly from China. It usually takes several weeks for these scales to arrive in your mailbox, but so far it has always worked out for me. These scales offered there frequently look exactly like the jeweler's scales you get in my home town - for 5-10 times the price.

,
However in the pricerange 0.001g for 50€ I do not find at manuals any figures for the error. Such I do find in the 200€ range.
On the other hand, from that 150€ surplus one could buy a decent calibration weight and test oneself...

Alan Johnson · Feb 14, 2020

My scale only measures to 0.1g but is reliable.IMO this is good enough.
To measure 0.2g phenidone I weigh out 0.8g, pour it in a heap and divide this into 4 with a piece of card.

Anon Ymous · Feb 14, 2020

As I mentioned earlier, making a 1% w/v solution of phenidone in hot propylene glycol is an easy way to get small fractions of a gram accurately. 1ml is 10mg. This solution has exceptional keeping properties, I still use one I made about 3 years ago, without any problems. The only other case where I might need very small quantities is potassium iodide. In this case, I weigh a small quantity, like 0,5g, make a solution of known concentration, then progressively use a small amount of this solution to make more dilute solution(s). In the end, I can use a reasonably large volume of the very dilute solution to get a precise amount of the few mg needed.

I only use one 100g/0,01g resolution scale I bought off eBay for about $10 years ago. It works fine and never needed anything else.

koraks · Feb 14, 2020

Anon Ymous said:
I only use one 100g/0,01g resolution scale I bought off eBay for about $10 years ago. It works fine and never needed anything else.

Same here, although I get mine from aliexpress, but same idea. I recently got 2 new ones since the previous one suffered from corrosion after a few years of use. No great loss. The new ones I got are 20g or 50g with .001 precision, but actual resolution is more like 0.005 at best. I only need about 0.01 resolution, but due to the inevitable inaccuracy of these cheap scales I picked the 1mg resolution ones so that the margin of error is hopefully within the boundaries I want.

Also the technique of making a 1% or 5% stock of phenidone in glycol or alcohol (I prefer glycol) is very convenient.

Randy Stewart · Feb 22, 2020

I have used an Ohaus triple-beam scale for decades, mixing B&W as well as C-41 and E-6 with no difficulty. When I retired a few years ago, in took home a Dymo electronic platform scale. I think it was about $20 at Staples. It seems accurate enough and would allow the measuring process to go much faster than the Ohaus. It immediate advantage is that will allow you to manage this equipment requirement for almost nothing to get started. I would take the money saved and buy a basic magnetic stirrer - nothing fancy, heater not required. Manual stirring chemicals into solution is the number one worst part of photo-chemical compounding.

Deleted member 88956 · Feb 22, 2020

Randy Stewart said:
I have used an Ohaus triple-beam scale for decades, mixing B&W as well as C-41 and E-6 with no difficulty. When I retired a few years ago, in took home a Dymo electronic platform scale. I think it was about $20 at Staples. It seems accurate enough and would allow the measuring process to go much faster than the Ohaus. It immediate advantage is that will allow you to manage this equipment requirement for almost nothing to get started. I would take the money saved and buy a basic magnetic stirrer - nothing fancy, heater not required. Manual stirring chemicals into solution is the number one worst part of photo-chemical compounding.

Thanks, I will look into the stirring options, first advice of its kind.

But, got myself this . Digital is convenient so I will likely have that too, this makes me smile.

KenS · Feb 23, 2020

Witold said:
Looking into mixing own B&W chemistry. Outside of lab quality volume measuring graduates/pipettes/etc , what type and max capacity of scale would you recommend (I see "precision" electronic scales are quite cheap, but cheap is not on my menu as reason to buy)
Have already a precision thermometer with very fast response, but what or any other measuring gear would be advisable?

Think.....
Face "dust-mask' and good quality 'one use" 'Disposable' gloves.

Ken

Mixing own chemistry

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