2023

Assembled blisters 
and shells used to imitate pearls

by Dr. M.S. Krzemnicki, first published in Facette 28 (May 2023)

Figure 1: Antique pearl necklace with a “pearl” in the centre, assembled from a blister with a polished piece of shell at the base. Photo: A. Chalain, SSEF.
Since historic times, natural pearls have been treasured and considered symbols of wealth and beauty. When harvesting (natural) pearls, one may find not only a pearl inside a shell, but also blister pearls and quite often blisters. A pearl has grown completely wrapped in a pearl sac in the mollusc, whereas a blister pearl is a pearl which connected at a late stage to the surface of the shell. Different to this, a blister is just a bulge in the shell surface, and as such much more common. Still, some of these blisters – specifically in nacreous shells – can show a very beautiful lustre and colour, and can be attractive for designers to create a “pearl” like an objet d’art. In some cases, however, this creativity is rather used to “create” an item with the fraudulent intent to mimic a pearl. With historic objects, it is however not always clear to what extent such creations were really fraudulent or just an expression of artistic creativity and skills. The first item described in this short note we received in the past months was an antique pearl and diamond necklace. This necklace was dominated by a central “pearl” set as a pendant (Figure 1). Radiography and chemical analyses on the smaller pearls confirmed them as saltwater natural pearls based on their “onion-like” internal structures. For the larger item, however, the radiography from the side was much less promising, as only curved layered structures were observed, furthermore with an evident cutting-line separating the upper part of this “pearl” from the base. Microscopic observation finally confirmed that this large “pearl” in fact was an assembled product (Figure 2), made from a nacreous blister at the top with a polished piece of shell as the base.

The second item is a Belle Époque pearl and diamond necklace (Figure 2) by Boucheron. Originally designed as a tiara in 1896, it was shortly afterwards transformed by Boucheron into a necklace and matching ear-pendants (1902). The 32 saltwater natural pearls in this jewellery have been carefully selected and exhibit beautifully matching button- to drop-shapes and a very ne pearl lustre. Their attractive colour subtly ranges from white to light cream. In addition to these qualities, part of these pearls show rosé and green overtones, poetically also referred to as the “orient of pearls”. These overtones are an iridescence effect visible on the surface of pearls and contribute greatly to the beauty of the described pearls.

Figure 2: The intersection line between the nacreous blister (at the top) and the polished shell (at the base) are clearly visible in this assembled “pearl” product. Photo: M.S. Krzemnicki, SSEF.
Figure 3: Pendant made of three curved shell pieces and radiography showing two of these pieces with a grey vertical intersection line where these two parts were glued together. Photo: SSEF.

The last item to be described here is the Fürstenberg pearl tiara. This tiara is set with 23 saltwater natural pearls of partly remarkable size in a historic design of the late 19th century. Based on the provided documentation, this pearl tiara was part of the jewels of Fürstenberg, a noble family from Southwestern Germany, hence its name. The pearls in this tiara are characterised by a beautifully matching drop shape and a ne pearl lustre. Their colour subtly ranges from white to light cream. The combination of well-balanced trace elements found in these natural pearls are characteristic of saltwater pearls.

The X-ray analyses of pearls in jewellery is often quite challenging for the analysts at the SSEF. This is especially the case when they are set in a rather rigid tiara with lots of metal mounting and diamonds. We were thus fortunate to have been able to analyse these pearls from the Fürstenberg tiara in a first round when they were detached from the main tiara setting. A selection of these radiographies is shown in Figure 4, revealing characteristic “onion-like” ring structures in these natural pearls. In addition, these radiographies show also different drilling situations, from being half-drilled to fully drilled.

Figure 4: X-ray radiographies of a selection of the natural pearls from the Furstenberg tiara. Photo: SSEF

The second item we received recently at SSEF was even more fascinating (Figure 3). This pendant was rather large with a maximal length of about 36.50 mm, containing as it seemed a large pearl of slightly baroque drop shape and kept in an “cage” of three metallic branches set with small old-cut diamonds. Originally thought to be a hollow pearl, also known as “soufflure” which sometimes are of exceptional size, it became quickly evident that this object had actually been assembled from three curved shell pieces to imitate a large natural pearl. From the distinct wear marks on the shell pieces, a rather old age might be possible. However, whether this item was truly historic, or made in an antique design with old shell pieces could not be established based on our testing.

Although disappointed by the fact that this item was not a natural pearl, the client was still happy to receive back the full information about this elaborately created objet d’art.

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