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Subject: Patina

Patina

From: Edgardo Pinto Guerra <xgardo>
Date: Saturday, September 30, 2006
Stefanie Scheerer <stefscheerer [at] yahoo__de>

>Krumbein defined Patina in its current application as "the sum of
>material and textural changes that occur in the surface zone of all
>materials, especially in objects of physical cultural heritage.
>These changes are caused by aging, material decay and environmental
>impact, including the biological environment". Involved are a
>surface layer of a few micrometers to several centimetres, where
>material and energy exchange between two open heterogeneous systems
>occurs. After the formation of a patina an intermediate
>stabilisation is reached. "If the patina formation leads to
>considerable mass increase of the substrate (deposits, subaerial
>biofilms, microbial mats, microstromatolite, sinter, silica skins,
>crusts black crusts, internal consolidation, cementation etc.) the
>mechanical and chemical influence of the mass increases may produce
>fissures and cracking, exfoliation, desquamation and other
>alteration processes".

In Italy (where we have buildings a little older than any the US) we
intend by "patina" the immediate (at most a few years) natural
physical alteration which the surface of a freshly cut stone or
manufactured element (brick) undergoes when exposed to the elements.
A meta-stable state which can last centuries. This occurs in the
first few micrometers but not deeper.

Patina is sacred--all else is decay and alteration to be treated.

Edgardo Pinto Guerra, Sarteano (Siena) Italy
Honorary Inspector, Ministry of Cultural Heritage


                                  ***
                  Conservation DistList Instance 20:19
                  Distributed: Monday, October 9, 2006
                       Message Id: cdl-20-19-007
                                  ***
Received on Saturday, 30 September, 2006

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