Originally Posted by Mackinaw
Years back, Xtol developed a rap of mysteriously dying. One day it worked fine, the next day a fresh dose from the same storage container produced blank negatives. Some folks say this is due to the amount of iron in the water though other folks traced it back to bad packaging (bad seams on one of the packages that allowed air in). I've never personally experienced this but, to be on the safe side, use only distilled water when mixing. Do a search on APUG if you really want to learn about Xtol.
Water quality around the world varies enormously. In Adelaide, the water is safe to drink but can taste a little strange or strong. Information on average water quality can be obtained for most municipal supplies, such as I found for Adelaide here:
I have tested water at my house, from the tap. It contains about 0.3-0.5 mg/L iron, almost all as ferrous iron and at times contains over 200 mg/L calcium.
The main issue that causes Xtol to lose activity suddenly is ascorbate oxidation. Xtol relies on isoascorbate to act superadditively with dimezone-S. Ascorbates are strong antioxidants and will scavenge oxygen from solution. Unfortunately the oxidation products of ascorbates do not develop latent silver images and do not present a colour change in solution. This explains what we already know empirically; Xtol can die without warning. The oxidation of ascorbates is catalysed by metal ions in water; particularly divalent cations (they are the 2+ ones). These include calcium and iron, the former common in photo grade chemicals, the latter common in tapwater.
I have titrated iron and calcium solutions into Xtol and tested its activity: I found that where the Xtol failed wasn't always predictable and is likely to depend on some fairly complex factors about the conbined load of ions in your water. 5L of xtol is not that expensive - just try it.
To avoid failure you can assess the activity of your Xtol a few ways:
1. Develop a Kodak Black and White Film Process Control Strip (CAT 180 2990) in your sample of Xtol and measure the density steps with a densitometer. Compare with your normal results and Kodak's recommendations.
2. In ordinary room light, using a 100 μL pipette from a scientific supplier, apply drops of Xtol, suitably diluted. Put a drop on, then another at 30s, another 1 min later, another 2 min after that and another 4 min after that, then fixing. Active developer will show a progressive increase in density. If you have a densitometer, you can work out an average, a 95% confidence interval and set criteria for use. Without a densitometer, as long as you look carefully in good light and know what it should look like, you'll be okay.
Don't blame me if tap water causes your Xtol to fail and results in the ruin of your images of a sasquatch, chupacabra, Judge Crater, space aliens or whatever.
Good luck and please report back to us about what you find.