One reason people don't do their own darkroom work, and one reason why many people stop doing their own darkroom work, is the amount of time it takes. One time-consuming task is setting up chemicals for the evening. These can be mixed up from kits or from scratch, but either way it takes time to measure and mix everything. It would be great to just mix up a gallon of each chemical, but then you need a place to store it all and the chemicals oxide and go bad quickly -- some in a matter of minutes. So each time you want to use the darkroom, you have to start all over.
There are methods to increase the longevity of chemicals. All of them involve removing the oxygen in one way or another. One method is to squeeze out the air in the storage bottle. This only works with plastic bottles and increses the possibility of a leak. You can even buy collapsible bottles, but these are very expensive. Another approach is to drop marbles into the bottle to replace the air, but this is very time-consuming and impractical with large bottles or bottles with small necks. Some companies sell jars of compressed gas. Since these gases do not contain any oxygen, they will not oxide the chemicals. Just fill the top of the bottle with the gas and close the top. A cheaper approach is to blow air into the bottle with a straw. This approach slows down oxidation, but does not solve the problem completely, since it does not remove all of the oxygen.
The best approach that I have found is to use boxed wine. The boxes come in a variety of sizes (and flavors) to meet your needs. The wine comes in a plastic/aluminun bag that collapses as the wine is removed. First, drink the wine. The dispenser pops off easily with a knife edge. Rinse it out with water. Then replace the wine with your favorite chemical. When filled (don't over-fill), replace the dispenser. Tip the box upside down, open the dispenser, and squeeze the bag to remove any air. Now you're ready for business. I use the 5 liter size and it makes my darkroom setup a breeze. I've stored D-76 and D-72 for months with no ill effects.
Last, but not least, make sure you carefully re-labels the wine boxes and store them in a safe place. You don't want anyone thinking that wine in stored in them.
One reason that chemicals "go bad" is that chemicals often come in kits and the entire contents are mixed at once. Let's say you have a one quart C-41 kit from Beseler, Unicolor or Kodak. When they come off of the production line their "suggested" expiration date is sometimes over 10 years -- it varies from chemical to chemical. But, of course, that's unopened. When you mix up the kit, the working solution will expire rapidly.
There are really two expiration issues here: 1. the expiration of the open concentrates, and 2. the expiration of the working solutions. I've found that the opened concentrates are good WAY past the suggested expiration date for the unopened bottles. And that WITHOUT putting marbles or carbon dioxide in the empty part of the bottles. (TIP: if you try the marbles technique, I recommend getting marbles at a hobby or florist store -- NOT the regular game marbles. The florist marbles are smaller and more likely to fit in the small tops of photo chemical bottles.) So if you buy the one quart size bottle, the shelf life of the opened, partially used concentrates should not be a problem.
You can solve the problem of expiring working solutions by mixing only what you need. Let's say you have two rolls of 16mm film. I'll only need 6.5 oz of working solution in my Yankee tank -- I develop one roll at a time, so I can reuse the chemicals. I dilute my C-41 chemicals 1+1 from what Unicolor recommends, so I'll only need about 1/15 of an ounce of Develop Part C, for example. That's about 2 milliliters. I pull out my set of syringes and draw off just what I need. At the end of the night I don't have any working solution to store, so working solution storage life is not a problem. If you mix the entire kit, you WILL have a big storage problem.
Just make sure that when you buy the chemicals that the expiration date is not getting close. If you order through mail order this can be a problem. The clerk will probably give you the oldest stuff they have. Get kits that are 100% liquid. If you get one that has powder(s) in it, it's best to mix all at once, since powders can separate in the package. And get a separate syring for each chemical -- NEVER put a syringe used with one bottle in another.
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