I found this from Rebecca about Ghost Images on Glazing which was around some time back but it might be relavent to this topic.
thought this might be of interest to some of you - it's about those ghost images that one often finds on the inside surface of glass. It would seem that there are various explanations, depending on what is actually in the frame and/or the composition of the glass.
This is copied from the Conservation Distribution List.
"Date: 18 Jul 2003
From: Niccolo Caldararo <caldararo@aol.com>
Subject: Salt on glass
This is in response to Bill Wiebold's and other comments and questions about ghosting images and salt on glass. This was an area of interest of mine when Walter McCrone brought up the issue of the image on the Shroud of Turin in his criticism of the idea that it was a natural occurrence.
I was investigating transfer images relating the microenvironments inside frames. This was a subject that Margaret Holben Ellis had also been working on and had discussed in her 1987 book on the care of prints and drawings. We often see these as negative images of the art transferred to the glass. I was concerned that this might
result in degradation of the image media, and sought to understand the components of the ghost image.
Ms. Ellis published a very striking image transferred to glass in her book and Marilyn Kemp
Weidner published another remarkable example in her article on the results of poor framing which appeared in Studies in Conservation,
v. 12, n. 1, 1987. I republished both in my article with T.B. Kahle which appeared in Restauro in 1989, v. 4.
Luckily I found that scientists at the Conservation Analytical Laboratory of the Smithsonian had studied this phenomenon and had a
number of reports available from the Lab's library (Padfield, Erhardt and Hopwood, ms).
Their analysis found that the substance
in cases they studied was mainly "...sodium chloride and an organic material with surfactant properties". (probably soap - Rebecca's insertion) The salt was mainly derived
from the salted silk of the framed object.
I thought that in most cases, like those in the images produced by Ellis and Weidner, the
transfer's agency was by the interaction of peroxides and hydroperoxides derived from the degradation of matting materials.
Vincent Daniels remarked in personal communication that such transfers are likely to arise from a drying oil which may explain
why we see such images often on the glass of framed prints.
Niccolo Caldararo
Director and Chief Conservator
Conservation Art Service
------------------------------
Date: 17 Jul 2003
From: Alan Derbyshire <aland@vam.ac.uk>
Subject: Salt on glass
I have also seen crystals and droplets on the inside of portrait miniature cover glasses. I assume that this is due to deterioration of the glass and that the crystals are alkali salt deposits.
This is a well known phenomenon due to the original composition of the glass and environmental conditions.. Due to their hygroscopic nature these deposits can absorb moisture under humid conditions forming droplets
but strictly speaking this is not 'condensation'.
On sealed miniatures the outside of the glass is often cleaned but the inside of the glass--because it is difficult to get at--is often left
undisturbed. As Bill Wiebold points out it is very common on French miniatures, 18th and 19th centuries but these crystals/droplets are also common on English miniatures.
If the condition is extreme it may be appropriate to consider replacing the cover glass as it would
be very difficult to control the relative humidity at which glass deterioration occurs or re-occurs.
This condition should not be confused with crystal formation on the ivory miniature itself, which is a separate phenomenon and due to the formation of magnesium phosphate salt deposits migrating from the ivory under conditions of high humidity. Examples of these crystals have recently been analysed using Raman microscopy.
Alan Derbyshire
Senior Conservator
Victoria and Albert Museum
London
------------------------------
Date: 21 Jul 2003
From: Loren C. Pigniolo <misterpuerh@earthlink.net>
Subject: Salt on glass
The recent discussion of salts appearing on the inside of framed works suggests to me a problem such as has been noted in relation to glass deterioration, especially in daguerreotype cases. The mention of this problem in relation to miniatures strengthens the connection in my mind. It would seem to be worth investigating whether a similar problem might be occurring in this instance.
The patterning in relation to the framed image might be explained by temperature gradients within the package, as discussed by Tim
Padfield in his articles "The Hunt Ball," and its sequel, "How to protect glazed pictures from climatic insult." These articles, and
others, are available at <URL:http://www.natmus.dk/cons/tp/>
I am most interested in what you discover, so please report your findings to the list.
Loren C. Pigniolo
Graduate Student, School of Library and Information Science
San Jose State University, San Jose, California"
Rebecca
[ 07-21-2003, 11:08 PM: Message edited by: Rebecca ]
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