What we know about amber imitations
Imitation - ( a counterfeit; copy ) designed to imitate a genuine or superior article or thing.
(Random House Unabridged Dictionary, © Random House, Inc. 2006 )
Forgery - the production of a spurious work that is claimed to be genuine (Random House Unabridged Dictionary, © Random House, Inc. 2006) Both natural resins (copal and contemporary resins) and synthetic resins have been used to produce Baltic amber imitations.
Resins
Amorphous natural or synthetic polymers, thermoplastic or chemically or thermally hardened, insoluble in water, liquid (with high viscosity), semi-solid and solid.
Natural resins are produced by the resin-forming cells of many plants and contain a mix of organic acids, alcohols, phenyls, esters and hydrocarbons. They harden when exposed to air. Natural resins include copal – a natural fossil resin from 10 thousand to 5 million years old. They appear in many parts of the world (to learn more, see: Fossil resins).
Synthetic resins are produced in polymerisation reactions (chiefly polycondensation) of various chemical compounds.
Use of resins:
- natural resins in ornamental art, medicine, cosmetic industry;
- natural but mainly synthetic resins for the production of lacquers, glues, laminates, ion exchangers, insulation materials, machine components, everyday objects.
Synthetic resins began to be used as amber imitations as early as in the 19 th century. These were nitrocellulose materials, synthetic casein materials, phenyl-formaldehyde resins, phenyl resins, carbamide-formaldehyde resins. In the 20 th century modern synthetic resins, such as polyesters, methyl polymethacrylate (Plexiglas) and others were introduced.
In terms of their reaction to heating, synthetic resins can be divided into:
a) thermoplastic materials which change their shape in high temperatures: celluloid, novolak, Plexiglas, some polyesters;
b) chemically or thermally hardened materials, which harden irreversibly: Bakelite, resolan, galalith, non-saturated polyesters.
Selected synthetic resins used to make amber imitations
Celluloid - nitrocellulose – the product of the esterification of cellulose with nitric acid, mixed with camphor and dyes. It imitated amber, ivory, horn and tortoiseshell, and was also used for cinema film, eyeglasses rims, toys and piano keys.
Properties:
- thermoplastic, shape change possible in water at a temperature of 80°C
- refractive index: 1.495-1.9
- density: 1.3 g/cm³ (transparent) to 1.80 g/cm³ (coloured)
- flammable, burns with a bright flame, gives off the scent of camphor upon slow burning or strong rubbing
- soluble in acetone, methyl alcohol
- low resistance to ageing.
Not used anymore due to its harmful impact on health and flammability podobnie jak celuloid.
Cellulose acetate - product of the esterification of cellulose with acetic acid anhydride.
Used similarly to celluloid.
Properties:
- thermoplastic
- refractive index: 1.490-1.505
- density: 1.3 g/cm³ (transparent), 1.9 g/cm³ (coloured)
- average flammability, burns with a bright flame, gives off the scent of acetic acid upon slow burning or strong rubbing
- soluble in acetone, methyl alcohol
- low resistance to ageing. Not used anymore due to its harmful impact on health and flammability
Galalith - (carbamide-formaldehyde resin – amino plastic) the product of the condensation of casein (an ingredient of milk which coagulates when treated with acid) with formaldehyde. Material widely known under many names (there were 55 trademark names for it in 1934), artificial horn. It imitated amber
Properties:
- thermohardening
- refractive index: 1.54-1.5
- density: 1.32-1.39 g/cm³
- low flammability, goes out after removal from flame, carbonises completely, gives off the scent of burnt protein - a drop of nitric acid causes bubbles or cloudiness.
Phenyl-formaldehyde (formaldehyde) resins (novolak, resolan, Bakelite) are produced in very complex reactions dependent on: the type of phenyl and aldehyde used, the ratio between these substrates, the pH of the reaction environment and its temperature. Thermoplastic resins, novolaks, form in an acid environment, while resolans, hardening plastic resins, in a base environment. These resins are used in their pure forms or following modifications. They were used on a mass scale before World War II to produce imitation amber products, including decorative pieces and smoking articles.
Novolaks - obtained in an acid environment with a small predominance of phenyl over formaldehyde. Used to produce necklaces with a beautiful cherry colour and varying degrees of transparency to imitate so-called antique amber.
Properties:
- thermoplastic
- soluble in alcohols, esters and ketones
- low resistance to light and water - low flammability, go out after removal from flame, give off the scent of phenyl.
Resolans - obtained in an base environment; they differ from novolaks in their containing free hydroxymethyl groups. Commonly used to make jewellery before and after World War II.
Properties:
- thermohardening
- refractive index: 1.54-1.70
- density: 1.25-2.00 g/cm³
- soluble in alcohols, esters and ketones - flammable, go out after removal from flame, give off the scent of phenyl.
Bakelite - made from a pressed mix consisting of 30-60% resolan or novolak and brittleness-reducing fillers (e.g. wood flour) and dyes. Asbestos was added to Bakelite in order to improve its mechanical resistance, while its thermal resistance was improved by adding improved rock dust, graphite or other chemicals. Known as African amber.
Resins which were mixes of phenyl, formaldehyde and other chemicals were not only harmful to the people who produced the resins and the products made from them, but also to the product's users, e.g. pipe mouthpieces caused irritation to the mucous membrane. The manufacturing of products from such materials has been severely restricted .
Modern materials used as amber imitations
Polyesters - the products of the condensation polymerisation of multihydroxide alcohols and multicarboxyl acids or their anhidrides. Polyesters can be very different from each other. Unmodified saturated polyesters are non-hardenable thermoplastic polymers. Modified non-saturated and saturated polyesters can be hardened through condensation or addition polymerisation.
Properties:
- some thermoplastic, some thermohardening
- soluble in: acetone, chloroform, tetramethyl oxide and benzene
- low flammability, continues to burn after removal from flame, gives off the scent of styrene.
Used to make microscope preparation – a fragment with an inclusion is coated with polyester resin. Small grains of amber embedded in polyester resin make the material polibern , which is used to make vases, lampshades, ornaments, etc.
Bernat/bernite - a mix of polyester resin and amber powder (natural amber powder yields light yellow products, powder from amber baked in ambient air yields reddish products, powder from amber baked in nitrogen yields green products which retain the transparency of resin) used for the making of gemstones, necklace and bracelet components.
Methyl polymethacrylate ( Plexiglas , perspex, diacon) – widely used material.
Properties:
- thermoplastic
- refractive index: 1.50
- density: 1.18-1.19 g/cm³
- soluble in acetone - burns with a bluish flame, gives off fruity or floral scent.
Epoxy resins - usually made of epichlorohydrin and bisphenyl A. Crosslinking (hardening) takes place with the use of hardening agents. Used to make a coating on soft young natural or fossil resins in order to harden their outside surface or to improve the properties of melted amber for industrial purposes.
Properties:
- chemically hardenable - low flammability, go out shortly after removal from flame, give off a characteristic sweet scent.