Precious Metals & Materials Guide


Why pick Astrea’s fine quality jewellery for yourself or a gift for someone special?


Precious metals

We use only precious metal as a basis of our jewellery: Sterling silver and 9ct and 18ct gold.

All products are described on the website with an accurate description of the materials used in their production – under the product specification tab on each product page along with dimensions of the jewellery. Also please carefully check the jewellery measurements you are ordering as most of our styles are fine and delicate designs for that elegant contemporary look.

Hallmarking Precious Metals

Our suppliers work with the Birmingham Assay Office and their chart gives the hallmarking laws for the UK:

Birmingham Assay Office
1 Moreton Street, Birmingham, B1 3AX
0121 236 6951

In the UK, hallmarking precious metals of a certain quality is a legal requirement. In fact, the Hallmarking Act 1973 makes it impossible to legally market your precious metal goods without hallmarks, unless exempt, although the standards must still be followed. It is also a legal requirement for sellers to display a copy of the Act at the point of sale (see Hallmark Guarantee on our website) using the link below:

Link Hallmark Guarantee 

As silver, gold, palladium, and platinum are very rarely used in their pure form within jewellery pieces, it’s required that the hallmark is used so that customers can identify and be confident of the quality of the goods they are buying.

Exemptions To Hallmarking

Precious metal pieces below a certain weight do not require full hallmarking:

  • Silver 7.78g
  • Gold 1.0g
  • Platinum 0.5g
  • Palladium 1.0g

Please note that these weights exclude that of any stones and are ‘per piece’ so relate, for example, to a single earring without its butterfly back. Although all items sold as silver have to (and do) comply with the above standard, many of our products are exempt from full marking but will still usually be marked either 925, SIL or SILVER.

What Is Sterling Silver?

Sterling silver is a metal alloy made of 92.5% pure silver mixed with 7.5% other metals – usually copper or zinc. Because pure silver is so soft, it is combined with these other metals to make it more durable for use in jewellery. To identify the percentage of pure silver in the alloy, the number 925 is stamped discreetly on the jewellery as a quality mark, alongside the sponsor’s mark and a symbol identifying the place of assay (an anchor for Birmingham). There’s no difference between real silver, sterling silver and 925 silver – they’re the same silver alloy, just by different names.

What is oxidised silver?

A piece of blackened or oxidised silver that is true sterling silver but where just the surface has been intentionally darkened by introducing it to a chemical process giving it a gun metal lustre. This patina, a surface colour that occurs when the silver is introduced to sulphides, is an acceleration of the natural tarnishing process. A layer of silver sulphide forms on the exterior of the metal giving it a blackened look

What Is Gold?

Here’s how they are broken down:

24 carat gold

The ultimate gold carat – it doesn’t go any higher than this. It’s the purest form and, in practical terms, consists of 99.9% gold. It is naturally yellow and highly valuable, but very soft and malleable, so it is not usually used to make fine jewellery or intricate objects.

22 carat gold

Consists of at least 91.6% gold and so is highly priced. It is also very soft, so it’s not ideal for stone-set jewellery, being more suitable for plain gold jewellery such as wedding bands.

18 carat gold

Contains 75% gold, with the rest made up of other more durable metal alloys used to change the colour and add strength. White metals will be added to create white gold with copper added to create rose gold. 18ct yellow gold is appreciated for its radiance and is much warmer and brighter in tone than 14ct and 9ct gold – but, with its high percentage of gold, it still comes at a higher price.

14 carat gold

Is at least 58.5% pure gold and has a warm yellow hue. It is more affordable than 18ct gold, making it a popular choice.

9 carat gold

Has 37.5% pure gold; it is the most affordable form of gold jewellery and portrays a light-yellow hue. Its higher percentage of other metals makes it stronger and more durable and particularly suited to the creation of jewellery. The lower gold content inevitably leads to more affordable prices.

Gold plating

When a product is referred to as being gold-plated this indicates that the article of jewellery is electroplated or mechanically sheathed with gold, either yellow or rose in colour. The quality of the gold used is typically 10, 14, 18 or 22 carat.

Pieces we describe as ‘gold-plated’ have gold plating over a sterling silver base. These pieces will therefore be correctly marked as silver.

Information about the carat rating and plating thickness is given in the product specification description of each individual item as these vary.

Gold Plating, Plating Thickness 

Heavy Gold Plated: > 100 micro- inch (>2.5 micron)

Gold Plated: > 20 micro-inch (> 0.5 micron)

Gold Electro-Plated: > 7 micro-inch (> 0.175 micron)

Gold Wash/Flashed: < 7 micro-inch (< 0.175 micron)

Standard gold plating is usually about 0.5 to 1 micron and is adjusted to account for different rates of wear – bangles and rings are subject to more wear than necklaces and pendants. Conversely, earrings are not exposed to heavy wear rates and so are often just flash plated – proven to result in a suitably robust product while keeping prices affordable.

Finishes And Coatings 

Rhodium plating

Rhodium is a rare and precious element that can be 10 to 25 times more expensive than gold. Rhodium is a member of the platinum group of metals and is silver-hued, highly reflective and does not tarnish or corrode. Some of our products are rhodium plated. This creates a slightly grey finish to products and rhodium resists tarnish, is highly durable but is becoming increasingly expensive.

Protective coatings


E-coating, aka electro deposition or electro-coating, uses an electrical current to cover a metal surface with an organic lacquer. The technique effectively covers every part of the jewellery piece so that it’s left with an even and consistent coat that will help preserve the colour of the plating and extend the life of the piece.


This is a simpler form of the above which is intended purely to minimise the possibility of tarnish, again by electro-coating.

Other protective coatings

Nano-molecular protective treatment – a coating applied to some products from one manufacturer and developed as being similar to E-coating but of higher performance.

Passivation coating – similar to the above but from a different supplier.

REACH Regulations

Jewellery is subject to a health and safety regulation, specifically The EU (Restriction, Evaluation and Authorisation of Chemicals) (UK REACH from 01/01/21). A regulation which has various Annexes that relate specifically to jewellery (Annex XVII n. 23, 27 and 63).

REACH restricts many potentially hazardous substances. Those relevant to all parts of jewellery are nickel, lead and cadmium.

Cadmium: equal to or greater than 0.01% by weight

Nickel: Rate of nickel release (migration limit):

  • less than 0,2 μg/cm²/week for jewellery intended to be inserted into pierced ears and other pierced parts of the human body
  • no greater than 0,5 μg/cm²/week for jewellery intended to come into direct and prolonged contact with the skin

Lead: equal to or greater than 0.05% by weight

We ensure our suppliers follow compliance in the following way

  • Members of the Responsible Jewellery Council ( third party audit of processes).
  • We work only with audited manufacturers who commit to compliance with each order placed.
  • Regularly sample items under hallmarking weight in-house using specialist equipment. All products from new suppliers are tested.

Stones And Materials


Modern marcasite comes from the mineral pyrite, which is a beautiful, metallised stone composed of iron sulphide.

Marcasite jewellery refers to the gemstone, but it also means a type of jewellery – setting tiny pieces of pyrite in designs into silver. Pyrite is extremely brittle when cut, which is why facetted stones tend to be very small. Our marcasite jewellery is set in sterling silver.

Freshwater pearls

We use

  • natural freshwater pearls in many of our pieces. Natural freshwater pearls are formed within mussels living within freshwater. They’re durable with an untreated, natural shade of white which won’t discolour if properly cared for.
  • cultivated real pearls create a rounder, cleaner shape.
  • faux (or imitation) pearls are occasionally also used if pieces are at the affordable end of the price range. They’re man-made from glass, ceramic or plastic coated with a pearl-like varnish, designed to look like real pearls.



We use only natural amber. Amber is a natural product formed from the fossilized resin of ancient trees living 25 to 50 million years ago. We use cognac, green and yellow in our products.


Natural stones

Many of our products feature natural stones in their description. Where named this is a natural stone. Stones include natural amethyst, blue topaz, onyx, green agate, chalcedony, etc. These are stated clearly in the product specification description and categorised as ‘Natural Other’ on the website.

Synthetic stones

We use some synthetic stones in our products such as synthetic rubies or sapphires. This is stated clearly in the product specification description and categorised as ‘Synthetic Other’ on the website.

Cubic zirconia

Cubic zirconia, or CZ as it is widely known, is a man-made diamond substitute which displays many of the desirable features of a diamond without the expensive price tag.

Cubic zirconia is made from zirconium oxide which is heated to extreme temperatures and then cut to produce maximum reflectivity.

Like diamonds, CZs are graded in quality and are sold commercially ranging from ‘A’ quality to ‘AAAAA’ quality.

CZ’s come in all colours and cuts.


Some of our products incorporate small natural (mined) diamonds. These are sourced from reputable suppliers and either have an identification number as a natural stone or, if very small, an assurance from the supplier as to their provenance and genuineness.


We use reconstituted turquoise in most products that feature turquoise. Turquoise in the form of chalk is crushed into a powder and mixed with plastics, dyes, and resins to form the compound known as reconstituted turquoise. This offers the appeal of natural turquoise but at an affordable price.

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