Finally got a camera and chemicals. I've bought Ilford Multigrade Developer and Ilford Rapid Fixer to be used with the Harman Direct Positive paper.
Just a couple of questions:
• Are the chemicals diluted or used neat? If diluted, are they used once then thrown away?
• Is there a way of knowing when the chemicals are 'spent' and need to be thrown away or do you just know when it stops working?
What you need to bear in mind, is there is enough active developer within your dilution/working solution, especially as there is such a small amount of liquid.
Oxidation will occur just be being exposed to the air, and agitation will accelerate that - so carrying a partial used container of dev around to then make up your working solution on location, is going to cause variable results, especially as it gets used up, i.e. there's less developer, it's older, and it's sloshing around in the container with more air in it.
If you want to reuse chemicals, you'll notice they discolour, and that is something you'll observe as you learn. Given you only use 20ml per syringe and the container is 1 litre, you can afford to use fresh chems each time.
If you want to avoid oxidation in the container, get some concertina chemical storage containers, so you can exclude air as you use the solution up.
I occasionally reuse working strength chems on location, but generally I'll take enough to develope a set number of shots plus enough for 1 or 2 extra for unplanned shots, and take that in the Pinsta travel bottles. Unless I was going away for a few days, I rarely take my main diluted solution, and I never take my main bottle.
I often reuse fix, 2-3 times but you need to factor in how much dev is carried over into the fix, as this will kill it, or at least keep topping up with fresh working solution. Again you are only using 20ml, so it's not exactly expensive.