Limestone is very durable and is an extremely good choice for a fireplace!
However, limestone is also rather soft and
relatively porous, so it does require care from the householder to
prevent stains and grubby marks spoiling the surface - especially for
new limestone fireplaces!
A few important points for first time buyers!
Your limestone fireplace should be chemically
sealed with a good quality sealant. The better sealants do not change
the colour of the limestone to any degree, but prevent easy penetration
of possible stains from getting into the stone. Your fireplace supplier
should either seal your fireplace for you, (probably at extra cost) or
provide a tin of liquid sealant for you to paint over the surface
yourself (also probably at extra cost). These sealants cost around £20
or more per tin, so if you see one for much less, don't use it, as it
may not be good enough, and could darken your limestone fireplace
colour!
If you have a limestone hearth, this should be
sealed twice. Leave the first coat to completely dry and then add the
second. Make sure you do not apply too much sealer, as this could cause
a change to the surface if soaked!
You may have to repeat the complete sealing
process after about six months or a year, especially if the fireplace
is for solid fuel. After that, your limestone fireplace will probably
not require any further chemical sealing.
Cleaning Limestone Fireplaces
The best way to clean off a grubby mark from your
limestone fireplace is simply to use a clean cotton cloth dampened with
very dilute washing up liquid. Do not soak the stone though!
If you have coffee or wine etc, spill onto your
limestone fireplace surface don't panic, just clean it off thoroughly
with a dampened cloth and everything should be fine.
A number of things not to do:
Never use wax or spray polishes on a limestone
fireplace, as these products can darken the surface of the limestone
and create patches.
Never use kitchen or bathroom cleaners, as they could react with the limestone surface.
Never allow cigarettes to be placed on the stone surface, the heat could cause a brown scar.
Never stand vases with flowers directly on the limestone surface, as this could cause a permanent ring mark!
Never stand red wine, tea or coffee etc, directly on your limestone fireplace -stains and ring marks could result!
Never stand coal or logs directly on the fireplace surface - damage and stains may result!
Never plaster down to, or on to a limestone fireplace - the stone will take up colour from the plaster. 
