It's all about... Lime

This week is National Science and Engineering Week at the Roman Baths and I have been charged with donning my other hat and talking to you all about Lime (not the little green citrus fruit)…..

So what is Lime?
Lime is a general term given to a number of compounds containing Calcium. This blog will be focusing on Quicklime and Slaked Lime. Quicklime is a white caustic alkaline substance consisting of Calcium Oxide, which is obtained by heating Limestone (Calcium Carbonate). Slaked Lime is a white alkaline substance consisting of Calcium Hydroxide, made by adding water to Quicklime and it is this form that is predominantly used in traditional building methods to make plaster, mortar and limewash.

Calcium Oxide Molecule

The diagram below shows clearly how Limestone or Chalk - Calcium Carbonate - turns into Quicklime (Calcium Oxide) after burning or heating. If water is then added it turns into Hydrated Lime or Slaked Lime (Calcium Hydroxide). The cycle is complete when it reacts with Carbon Dioxide from the air around it, turning it back into Limestone. This process is known as the Lime Cycle.

The Lime Cycle

So why is Lime so important in historic conservation?
Buildings pre 1900 would not have been built with modern cement (with few exceptions in the late 19th century), but with a lime mortar. In order to conserve and repair these buildings, it is essential to use similar materials such as lime mortars, lime plasters and renders.

Does it have to be Lime?
Modern buildings generally rely on an outer layer to prevent moisture penetrating the walls, whereas buildings constructed before 1900 generally rely on allowing the moisture, which has been absorbed by the fabric, to evaporate from the surface. In essence, old buildings exposed to the elements are continually absorbing moisture, and the ability for the moisture to evaporate again is crucial to the welfare of the structure. Lime based building material is perfect for this two way exchange.

Using modern cement based mortars and plasters in traditional buildings risks locking-in the moisture, which could result in dampness internally and spalling of brick and block externally, as a result of freeze and thaw.

Pop along to the Roman Baths today, Wednesday 14th March 2012 between 4pm and 8pm and see me in action. I will be on hand to answer any of your lime based queries and demonstrating how we use lime based building material on-site.

For more specific information on applied lime based building material here at the Roman Baths, take a look at my previous blog – It’s all in the mix.

http://bathsbloggers.blogspot.com/2011/05/its-all-in-mix.html

Helen Harman - Collections Assistant

A Gorgon's Head?

Gorgon's Head?

I have puzzled over an alternative interpretation as to who/what the image in the centre of the Temple Pediment really is. I am sure that the character who dominates the centre is almost certainly not a Gorgon. For starters it’s a male; the only male Gorgon is Nanas (guardian of Zeus) who would have no relation to this site. Most importantly though, where are the snakes!? I see some thick wisps of beard but certainly no snakes. So who is this character?

The obvious choice for me is Neptune, not only does the aged bearded face resemble him but he is the God of water. The Romans had no natural explanation for hot springs such as those found at Bath, so to turn to a supernatural source for worship was not uncommon and here the deity of water makes perfect sense.

Artist illustration of Temple Pediment

If you look carefully you will see nestled in the corner of the pediment are Tritons; half men half fish creatures who were the servants of Neptune. If this image is not of Neptune then who is he? This mysterious figure could be any one of a number of water deities, perhaps the God Oceanus?

Mildenhall Silver Plate

Another theory is that in an effort to endear themselves to the native populous they governed, the Romans often amalgamated ‘their’ Gods with local ones (our very own Sulis Minerva is a great example of this.) Perhaps this is what happened here but current knowledge of local deities is very limited and offers no obvious links.

Next and perhaps most controversially it might be Mithras. This Eastern God was popular amongst the Romans at the time the Baths were active. Worship of Mithras was most popular among the military; soldiers of course built the Baths. The story of this God is also entwined with that of Sol (the Sun God).

As the Roman Baths website tells us the discovery of the Gorgons Head Temple Pediment “confirmed that the Roman site at Bath was unusual and attracted special interest to the site”.
Is it right to keep referring to this image as a Gorgon when it is clearly an interpretation that can be questioned? It’s hard to believe that once the head of Sulis Minerva was believed to be that of Apollo, What do you think?

Heath Meltdown