Re: KRS - artificial weathering

From: zolota (zolota3_at_REMOVEshaw.ca)
Date: 09/18/04 

Date: Sat, 18 Sep 2004 06:42:05 GMT

"Eric Stevens" <eric.stevens@sum.co.nz> wrote in message
news:evalk051svrvqch0um8ebgjhn2nt4ubn96@4ax.com...
> On Fri, 17 Sep 2004 06:11:45 GMT, "zolota" <zolota3@REMOVEshaw.ca>
> wrote:
>
SNIP

>>
>>A salt-ice-water mix will have a depressed freezing temperature but mixing
>>the three can only be the sum of the sensible heat of the mix.
>
> Sorry, you have forgotten both latent heat and heat of solution.

I appologize for simplifying it. Adding NaCl salt to water lowers the
temperature by three degrees, canceling the change in my example below.

>
>>If you
>>started with 1 kg of ice at -9 degrees C, 500 g of ice water, and 100
>>grams
>>of salt you will arrive at -6 C or so. If I was faking a surface I'd just
>>drop the hot rock in ice water, it's the rate of cooling that does the
>>most
>>damage. A rock left outside overnight on a three dog night then hit with
>>boiling water would also spall! If anything these methods may be too
>>strong,
>>but the serious forger would never have left something she was not
>>satified
>>with.
>>
>>It also seems to me that some stone masons must have traditionally had
>>some
>>some methods of artificially aging rocks. Say for example that a church
>>wants to put an addition onto one side. The master with the reputation who
>>could age the rocks to look like the originals would be in demand. It's
>>probably a lost art today. Shall we all experiment with rocks using our
>>freezers and kettles?
>
> More likely confirm that my experience that stone masosn would rather
> freshen up the entire church to look like new is the more common
> practice.

I'm not sure, but in some communities the aged look is in. Gives the
building a respectable permanence. There is also the practical consideration
that a new wing on a building is one thing to change, but putting
scaffolding around the whole building and working on all of the surfaces
would run up the cost more.

>>
>>Despite what others say, a rock that had been in salt water would show no
>>evidence of the salt later.
>
> I never said that. What I was trying to pint out that Martin's attempt
> to induce frost cracking by using salt to create a freezing mixture is
> fraught with practical problems which he doesn't really understand.

Agreed. If you have heated a rock in a fire to 200 degrees, whether you
quench it to 0 or -5 degrees is rather trivial.

I decided to pust some ideas here to get feedback. Now I'll criticize
myself. Until the invention of explosives mining could only be done in rock
using one of few methods. If the rock is soft and a harder material is
available, it can be broken mechanically. This includes bone or flint tools
for scraping chalk out of tunnels in the search for flint nodules in
paleolithic times. The Egyptians used copper chisels on limestone, Easter
islanders used hammers on the volcanic rock. The advent of iron tools made
this approach easier.

If the rock was hard then fires were built to warm the rock, followed by
quenching with water. The Egyptians used this method to mine gold in Nubia
(the Sudan) and the Germans were still using it 400 years ago in Bavaria.
The objective was to cause sudden shrinkage of the surface that resulted in
chunks and slabs to spall off. I can't imagine being the person who throws
the water and breaths the steam, but that was what slaves were for. Needless
to say overdoing it with the KRS would have resulted in a bucket of road
gravel. Still, alternate quenching with boiling water then ice water on the
surface to be aged would rapidly produce the mechanical wear that years of
winters would otherwise require for the same effect, both in terms of
individual crystals falling out and of sharp edges being rounded. Again, I
ask anyone to tell me how this action could be detected after the fact.

Z

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