[Leica] Water Chemistry for Dummies

[William Gower <w.gower@home.com>]

Martin (et al.)

You've gotten allot of Alchemy regarding your Watermarks. Now it's some time
for some Chemistry.

You happen to be blessed twice. Not only are you living in Columbus Ohio,
but also you happen to be drinking water out of the Upper Scioto watershed.
Looking at the geology of Ohio, I would take a hydrogeoloical stab and say
that if the city of Columbus is drawing water from a groundwater Aquifer,
then it's going to be of Silurian-Devonian genesis, possibly Mississipian,
maybe a mix from both.

This means the underlying bedrock is Carbonate (Limestone and Dolomite) with
some Sandstone in the mix. Great water for beer and Whiskey, crappy if
you're trying to prevent watermarks. If the aquifer is surfacewater (a lake
or river), it's still going to be influenced by the bedrock matrix.

It was nice that people told you to either (a) ration the Photoflo or (b)
give 'er hell ! It's important to know that when it comes to water
chemistry, everyone on this list has different water. What's going to work
for some isn't going to work for you. Vice versa. Technique isn't the issue.
Chemistry is. (Although, using your fingers rather than a squeegie is good
advice - just remember to wash the fix off your hands first.)

Look at your taps. Do you have white scale forming around your faucet? Do
you notice that the hot water tap has more scale than the cold water tap?

This is Calcium Carbonate. Unlike most minerals, the solubility actually
decreases with temperature. Calcium is the principal constituent of
"Hardness". Magnesium is the second. Iron is tertiary. You probably have all
three.

Calcium carbonate can be removed from water by heating. This is what we do
in the water treatment industry when we have to remove hardness for process
water. The incomming water is heated and hit with a lime slurry. The calcium
and magnesium settles and forms a sludge, then the water (devoid of the
majority of hardness) is sent for further porcessing.

Now go look at the heating element of your electric Kettle.

Water classified as "hard" forms a scum or precipitate in the presence of
soaps. Photoflo is a fancy soap =  hard water will form a scum or
precipitate in the presence of Photoflo.

Water is a wonderful, wonderful thing. One of it's more magnificent
properties is that it is highly polar and, because of hydrogen bonding and
other phenomena, it has unusually high surface tension - water forms
"droplets". Agents that can break this surface tension are classified as
surfactants or "surface-active agents".

A surfactant lowers the surface tension by interfering with the polar
hydrogen bonding on the water molecules surface, causing the water droplet
to collapse under it's own weight - this is the "sheeting action" we see
when water beads off a negative.

I don't know exactly what Photoflo is, but an educated guess would be that
it's an alkyl benzene sulfonate (a common synthetic surfactant). The alkyl
benzene sulfonate is similar to the carboxyl-hydrocarbon chains found in
good old-fashioned glycerin soap like mom used to use. Like I said before,
Photoflo is just a fancy soap.

What can you do? Well, a combination of Photoflo and deionized water or
distilled water is the best approach. If your water is really hard, multiple
rinses of deionized or distilled water will be necessary.

I would avoid "softened" water like Culligan is going to probably suggest.
The softening process uses an ion exchange resin to exchange hardness
(Calcium and Magnesium) for Sodium. You still have the salts in the water;
it's just that sodium won't scale up than Calcium and Magnesium. But it
still will leave deposits.

If you are so inclined (or any LUG'er for that matter) I can help you build
your very own water deionizer for a few bucks that will put this issue
behind you.

(If you haven't guessed already, this is what I do for a living. I'm an
industrial process chemist - my specialty is water quality management for
the steel industry.)

Martin - call your local water utility and ask for a fax of the historical
water analysis. If you want help deciphering it, drop me an e-mail.

Kind regards

William Gower