Re: KRS - artificial weathering

From: Eric Stevens (eric.stevens_at_sum.co.nz)
Date: 09/20/04 

Date: Mon, 20 Sep 2004 13:23:01 +1200

On Sun, 19 Sep 2004 22:08:30 GMT, "Martin Reboul"
<martin.reboul@SPAMFUKvirgin.net> wrote:

    ---- snip ----

>> >Undoubtedly you meant something else. What would this person look for to
>> >determine that the apparent aging is not genuine? How would she know what is
>> >real? What measurements would it take to show that the surface is at least,
>> >say, 200 years old?
>>
>> I've already said I don't even know enough about this subject to be
>> dangerous - except to myself. BUT - as I have said several times
>> already - I would look for the sub-surface chemical changes which are
>> part and parcel of weathering.
>
>By using dilute aqueous acids, far stronger than the normal, slight acidity of
>rain and surface water, that process of chemical change would also be
>accelerated. The crystalline structure is stress fractured by thawing/freezing,
>then degraded by chemical action as the acid creeps in and reacts with pyrites
>etc. No residues would be left if the stone was finally scrubbed and thouroughly
>risned with plain water, as any products of such reactions would be soluble. The
>two go together.

You continue to misst the point. Stone is permeable, even if only very
slightly so. Immerse a stone in a reactive solution and the reagent
will start to diffuse through the stone. If it meets anything it can
react with, it will, thereby effecting chemical change beneath the
surface. This will exhaust the local reagent and time will be required
for more to diffuse from the surface. The longer the stone is exposed
to the reagent, the further below the surface will the products of
reaction be found.

Using a stonger (even though still dilute) reagent at the surface will
make only slight difference. Apart from the fact that the different
concentration may produce different reaction products, the governing
rate at which the surface/sub-surface weaathering will take place is
still largely governed by the rate of diffusion. Increasing the
concentration of the reagent will speed things up slightly but when
dealing with a relatively impermeable stone like greywacke the depth
of the reaction crust is primarily determined by time. There is no
simple way you can quickly fake an ancient chemical weathering crust,
especially with the knowledge of the 19th century.

Eric Stevens

Quantcast