Collectors will sometimes come across a miniature painted on ivory
which has become 'warped' or even worse, cracked.
It is possible to repair cracks and if done well by an experienced conservator,
the repair can be virtually invisible.
We have noticed that many later miniatures
(late nineteenth and early twentieth century) suffer from warping because
the ivory leaf has been stuck
to a backing board and this seems to be a regular practice during this time. Bonding different materials with different
coefficients of expansion is not a good idea,
especially with a strong glue!
This is a miniature painted by Ida Laidman circa 1915 of an
unknown lady and it was badly warped.
The ivory stuck to a backing board was even pushing
the back cover away from the frame.
When the miniature was removed from the frame the extent of the
bend in the ivory is apparent
Not a task for the amateur, the backing card had to be removed by a conservator in order to save the miniature from further curvature and eventual cracking. The sooner a conservator is used to restore the flatness to the ivory, the better.
A new acid free backing card had to be cut with the ivory sandwiched between this and the glass, without being glued to it.
The miniature was re-assembled into it's cleaned frame and is now looking
much like it did when it was painted. We thought the lady had a
slight smile on relief on her face!
If you compare the ivory plaques of the Georgian and Revival periods are they the same? Wondering if they maybe cut differently or of different thickness and thus make them, during the later period, more prone to warping.
ReplyDeleteThank you for your interesting comment. When ivory was first used during the early part of the 18th century the ivory was quite thick (2 to 3mm) but the thickness of about 1/2 mm has been constant from the mid 18th century up to today. Continental miniatures seem more prone to cracking maybe because of the use of different elephant species or the circular shape which was used more than the oval shape miniature. The warping, seems to us, because of glueing the whole ivory to a backing board. During the 18th century and early 19th century the back support was usually taped to the ivory only around the edge thus not putting so much strain on the ivory from dimensional changes of the support.
ReplyDeleteMay I ask what percentage of your collection displayed degrees of warping? Of the total number of warped miniatures did all have glued backing cards or indications one was once present? I only have 24 miniatures and two are warped. None of my miniatures have glued backing cards But 24 is too small a test number. I am wondering if there are other reasons which may cause warping. Possibly acid or bacteria in the backing material. ..JL
ReplyDeleteHumidity changes will change the physical dimension of a material so if the backing board has a coefficient of expansion different to the ivory then the two materials will have an action similar to a thermostat principle. We remove any backing card attached to the ivory and make a new card which is taped to the front glass around the edges. This leaves the ivory supported but not constrained. Warped ivory will retain a memory and by a special method the humidity is increased on one side of the ivory causing it to warp in the opposite direction almost immediately. By repeating the warp back and forth for several times under controlled conditions and then placing the ivory in a special press for several weeks it will return to it's original flatness. We would add that such procedures should only be carried out by a trained conservator and do not recommend any collector to attempt such work. In answer to your question we have noticed more warped ivory on later miniatures attached to a backing card. We have never kept a record on numbers. If an ivory is warped and not attached to anything then we would say that it probably has had many years where the humidity levels either side of the ivory have differed, maybe due to the coldness of the front glass in cold houses? We always use acid free replacement card but your suggestion could well be valid and perhaps a conservator would have a view on this
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