DEAR TIM: In the log books of our historic light station,
the lighthouse keepers mention whitewashing, painting, and something called
calciuming. I have tried in vain to discover what that might mean. All I know
for sure is that it's something they did to the interiors of their dwellings.
The keepers' houses are brick and the interiors have horsehair plaster directly
on the brick walls, and plaster on the framed interior walls. Can you tell me
anything about calciuming? What was it? Why do it? How do you do it? Should I
still be doing it? Ellen Henry, MFA, Curator of Collections and Education, Ponce
de Leon Inlet Light Station, Ponce Inlet, FL
DEAR ELLEN: As much as I hate to say it, I believe the term
calciuming might be peculiar to those particular lighthouse keepers. It probably
is a slang term for a particular type of whitewash or plaster treatment applied
to the inside of the walls of their dwellings and possibly the actual
lighthouse.
The brilliant white finish on the Tawas Point lighthouse on Lake Huron could be a coating of pure lime. It dries pure white. There is a possibility pure lime was also used inside the house next to the lighhouse. PHOTO BY: Tim Carter
Because of the extremely harsh marine environment, they
needed a wall treatment that would not disintegrate. The constant humidity and
heat in your location would quickly cause regular finish materials to fail in
short order.
The biggest clue is the word calcium that happens to be the first part of
calciuming. Calcium is the principal element in lime. Lime is, of course, the
principal ingredient in whitewash, older mortars and plaster. Lime is created by
heating very pure ground-up limestone. The chemical formula of limestone is
CaCO3. The heating process disturbs the chemical makeup of the limestone and
drives off carbon dioxide. The resulting powder is CaO or quicklime and is
chemically unstable.
The lighthouse keepers could line the inside of the dwellings with limestone
rock, but something tells me they wanted a smoother finish. What's more,
installing solid rock walls is costly and labor intensive. But, if you
systematically apply layer after layer of thin liquid limestone that hardens on
interior walls, you get a smooth surface, it is hard as rock and it requires
minimal skill and labor.
This is the famous Ponce de Leon Inlet Light Station in Florida. It is a massive structure built to withstand all the ocean can throw at it. PHOTO COURTESY OF: Ponce de Leon Inlet Light Station - Ms. Ellen Henry, MFA - Curator of Collections and Education
Limestone is a very hard and durable rock. It can withstand
tremendous punishment from Mother Nature. By reversing the chemical reaction
once you have quicklime, you can make man-made limestone. Quite possibly this is
what the lighthouse keepers did.
The quicklime wants to react with other chemicals so that it can once again
be stable. The humidity in water vapor, regular liquid water and carbon dioxide
in the air around us readily satisfy the quicklime's desire for the lost oxygen
and carbon that left the limestone when it was heated.
So if the lighthouse keepers regularly mixed lime with water and possibly
some very fine sand, they would be periodically adding layer after layer of very
thin durable limestone to the inside of the lighthouses. I think this is what
was happening and when you stop and think about it, it makes perfect sense.
