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Small portraits - big problems

Read the story of how some of the tiniest artworks of Unique National Importance are preserved for posterity.

A whole collection of miniatures
Miniature paintings were sometimes used as jewellery, often in the form of a portrait locket, or hung for decoration in a small display cabinet. Despite the name, ‘miniature’ painting could vary in size from tiny portraits to larger scenes.

In some cases, there are special adornments on the front- or backside of the miniature, such as pearls, diamonds, enamel or even braided hair. Miniatures are often protected with custom-made glass – either flat or slightly convex – which tends to be hand-polished and hand-cut, and offers the added bonus of having a slight magnifying effect, allowing the tiny painting to be better seen.

The National Gallery of Denmark has a fine collection of approximately 430 miniatures.

Damaged miniatures
Despite their compactness and the protection offered by their glass covers, miniatures sometimes suffer damage to their delicate colour-layers. This can be due to, for example, impact, condensation, degradation of the binder in the paint, or fading of photosensitive pigments. These, and other, factors may result in flaking and eventually loss of paint.

Conservators record any damage to the miniature, assess the extent of any physical problems it faces and decide whether or not the object may need conservation treatment. During conservation of artworks, conservators may take the opportunity to conduct additional technical studies. In order to learn more about the specific conservation problems of miniatures, in 2007 the Conservation Department at SMK began working with an expert in the conservation of miniatures from the National Museum of Sweden in Stockholm.

Weeping glass and dramatic consequences
Condensation inside the miniatures is avoided by ensuring stable humidity in storage rooms and galleries. However, there is a particular problem which is faced by miniature glass. Over the last 400 years, glass has been produced in different ways and with different proportions of silica, which is a special type of mineral. Glass with particular proportions of silica can develop a so-called 'glass sickness'.

A detail of Horneman's miniature showing the weeping glass with the small drops on the inside.

The miniature Sophie Brun by Christian Horneman (ca. 1818). Dimensions: 7.6 x 6.3 cm. Watercolour on ivory.

'Glass sickness' can be seen as small droplets, which form on the inner face of the glass. The droplets that come out of the glass are very alkaline, with a pH of around 10. With such a high pH, if the droplet comes into contact with the paint layers of the miniature, it can be very harmful. There are currently no conservation methods that can stop this process in the glass. Consequently, the glass must be removed and preserved separately, whilst on the miniature it is replaced with brand-new custom-made glass. During this process, it is necessary to open the miniature for the first time since its creation several hundred years ago, to prevent dramatic damage to the paint.

Miniatures of cardboard and parchment
The tradition of miniature painting originates with medieval book illumination. The earliest miniatures in the museum's collection date from the 1600s. They are painted on paper or parchment (prepared calfskin), with matte and opaque gouache paint.

Gouache consists of finely-ground pigments – minerals and plant extracts with the addition of white for opacity – with gum arabic as a binder. This type of paint does not require as much water as watercolour, which is important as cardboard and parchment is extremely sensitive to moisture. The brushes used by painters of miniatures were specially prepared by grinding their tips so that the hairs became very fine – the finest brushes had only a few hairs, and were used for painting the flesh or details. The paint was often applied in dots, or 'stipples', which can be seen under a magnifying glass or microscope.

Ivory – a mirror for skin tones
The technique of painting miniatures on ivory comes from Italy in the late 1600s. Andreas Moller (1684-1762) was the first Danish miniature painter who used this technique in 1714. By the 1740s, however, the technique had become much more widespread in this part of Europe.

Ivory can be cut into very thin slices and then polished smooth with pumice. The thin sliver of ivory was usually reinforced by gluing paper, cardboard or even metal foil on to the reverse. One of the main advantages of ivory is that it can reproduce the effect of flesh tones extremely well. The surface is very delicate, so even fingerprints can cause damage to the water-sensitive paint.

Both thicker, matte gouache and transparent, shiny watercolour were used. The gloss of the watercolour is due to a relatively high proportion of gum arabic and honey, but too much binder can cause the paint to flake eventually. It is the conservator’s job to consolidate the loose paint flakes to the support if this happens. It is important that the glue used to reattach the paint flakes does not stain the delicate surface of the miniature. Therefore, conservators work with tools and brushes that are as fine and precise as those used by the miniature painters who originally made the artworks.

Barna Bengtsson with a miniature

Barna Bengtsson with a miniature.

New light on the delicate mini portraits in glass and frame
In the 250 years when miniatures had their heyday, many and varied materials and techniques were used to create them: from the stable, glossy, bright and sometimes lumpy oil-paint on copper of the early 17th-century, via shiny enamel and porcelain, to delicate colours such as watercolour and gouache on cardboard, parchment or ivory.

Despite new knowledge, faded colours cannot be saved or restored, so the amount of light a miniature is exposed to in its display case at the museum must be reduced to a minimum to preserve the works for posterity.

Written by
Barna Bengtsson
Paper Conservator

Updated: 26.apr.2018
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