Photographic chemicals are generally robust however they will lose their effectiveness over time. Exactly how long will be their shelf life is a variable. Developers tend to have the shortest shelf life. This is because the developing agents are relatives of benzene which was initially synthesized from coal. These agents have an affinity for oxygen. They readily react with dissolved oxygen that is in the water that constitutes the bulk of the developer solution. All developers contain preservatives that retard oxidation and neutralize the staining effect brought about as developing agents oxidize and revert to coal tar. These preservatives can only do so much, as time goes by; the developer solution oxidizes and turns black.

When we mix developers we generally start by diluting a concentrate to make a stock solution. The concentrate has a prolonged shelf life. The stock solution is likely good for about 6 months if full and well stopped up. If the stock solution bottle is not filled to the brim, its shelf life is about 2 months. If the stock solution is diluted to working strength (tank solution), its shelf life is reduced to about 24 hours. Stop baths, prepackaged have an indefinite shelf life. When diluted with water, the shelf life is about 3 days.

Fixer concentrates have an indefinite shelf life. When diluted with water to make a stock solution, the shelf life is about 2 months if in a stoppered full bottle. When diluted to working strength the shelf life is about 3 days.

Keep in mind, many of the concentrates are highly concentrated. They may be super saturated solutions. Thus concentrates many not be able to tolerate low temperatures because of the danger that the solutes may fall out of solution. Should this happen, solids appear in the bottles. Most times, warming the bottle will cause these deposits to re-liquefy.

We mitigate oxidation by squeezing the air out of plastic storage bottles or by dropping in marbles to displace the air in stoppered bottles. The developer and some other solutions can be ruined by prolonged exposure to light. We use brown or green storage bottles to increase shelf life. Old time darkroom workers blow into partially filled bottles and then quickly cap. The idea is, human breath is low in oxygen content. This is an unproven technique but it makes us old-timers feel better.

Let me add, the potions we use to process film and paper are very benign. The acids and alkalines are mild. The most prevalent odor is that of vinegar. If you are storing these bottles outside to protect your family from harm, you are exercising a super abundance of caution. Outside is OK provided these fluids are not exposed to high temperatures. Also, bright light should be avoided by the packaging.