Gübelin Gem Lab starts offering identification of filler type in emeralds

Beginning September 1st 2017, the Gübelin Gem Lab offers the determination of the type of filler material in emeralds in order to provide more transparency.

The increasing demand from end consumers for full disclosure and hence the request from jewellery brands and retailers for the determination of the type of filler used in emeralds have triggered this change of policy at the Gübelin Gem Lab. This new service is offered in all three permanent laboratories of the Gübelin Gem Lab (Switzerland, Hong Kong and New York), whenever requested by the client.

Fissures are commonplace in emeralds, even in high-end specimens and can affect the transparency and look of the stone. The practice of enhancing the visual appearance of emeralds by filling fissures with oil or resin is a standard procedure. Such fissure filling can improve the visual appearance of an emerald dramatically. This treatment is fairly well known to the public and generally accepted as a necessity due to the nature of emeralds.

A broad variety of substances are used for this treatment, characterized by different optical and mechanical properties, stability and durability. For this, we distinguish different groups of filler materials: oil, resin and wax.

Oil is a traditional type of filler in emeralds, used since more than two thousand years. Mostly of low viscosity it penetrates deep into the surface-reaching fissures. Oil can leak or dry out over time, losing its clarity enhancing effect. With the help of cleaning agents such as acetone, oil can be removed. Hence, oiling is a reversible and repeatable process.

Resins are a more modern type of filling material, used since the middle of the last century. Mostly synthetic, these resins are characterized by optical properties close to those of emerald, and, once applied in fissures, a high viscosity. This property makes the resin more durable and stable, and hence suitable not only for clarity enhancement, but also for stabilising lower quality material which otherwise would not be sufficiently durable for use in jewellery. Consequently, resin is applied mostly – though not exclusively – on lower grades of emeralds. Due to their more resistive nature, resins are harder to remove from fissures.

Wax, typically paraffin wax, is another category of filling material used in emeralds. Wax is solid at room temperature and not soluble in water. In the past, wax was the preferred substance used for clarity enhancement on emeralds from certain African origins.

On its Gemmological Reports, the Gübelin Gem Lab now distinguishes the following types of filling materials:

  • Traditional (oil-type)
  • Modern (resin-type)
  • Mixed (oil-type and resin-type)
  • Wax

The type of filling material is mainly determined by spectroscopic methods, i.e. FTIR and Raman, whereas the presence and extent of clarity enhancement is determined by microscopic analysis, supported by spectroscopic methods.

With the introduction of this service the Gübelin Gem Lab intends to provide the trade, brands, retailers and the final customer with the requested transparency, helping the buyer to get a more complete basis of information before making a binding decision.

For further information, please contact:
Daniel Nyfeler
T: +41 41 429 17 17