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Chelsea Filter

Chelsea Filter


Price: 24.50 Including VAT



Gem ID Book £25.00 instead of £29.50 £ 25.00

Gemstones book £15.00 £ 15.00

Add fine-focus pen torch £5.50 incl. VAT £ 5.50 incl. VAT

The original Chelsea Filter, as developed at the Chelsea College of Science and Technology in 1934.

Many stones appear to change colour when viewed through the filter. Originally designed for detecting synthetic emeralds, nowadays the Chelsea filter is an invaluable aid to identifying many other gemstones.

It can give an indication that you have an emeralds and aquamarines, though not a guarantee, since there is considerable variation in their chemical compositions (the amount of chromium that gives the green colour and the amount of iron that 'dampens' the effect through the filter).

It gives a very clear and spectacular result on blue stones coloured with cobalt. Since cobalt doesn't colour stones blue in nature, this is a sure-sign that you have a manmade stone (e.g. synthetic spinel) or glass.

With skill, it helps identify dozens of other stones. It's particularly useful when you have to sort large parcels of stones into 'probables' - then you have clues as to which tests to carry out next.

{Is it easy to use?}
USING it is very easy indeed. Shine a light (any pocket torch) on the stone, hold the filter close to your eye, view any colour change. You don't even have to hold the stone close to the filter (only the filter has to be close to your eye) so you can examine stones in museum showcases.

There is an instruction sheet supplied with the filter. However, in common with all gem testers, it does not provide an instant, easy and guaranteed identification of gemstones (the only 'easy' one is detecting cobalt-blue stones, which are synthetic…or glass) and you would be well-advised to buy a book about gemmology (see Further Information).

{Further information}

This is a standard gem tester used by gemmologists, it does not come with instructions, you are expected to know how to use it (a bit like a bicycle, it does not come with instructions telling you how to ride it).

If you are new to gemmology I strongly recommend the book Gem Identification Made Easy. This book systematically works its way through all the optical testers, telling you the theory behind them, what they will test, and how to use them. To get your discount (£25.00 instead of £29.50) tick "Add the Gem ID book" when you order the Chelsea Filter.

Here are more details of the optional extras you can add to this order:

Gem Identification Made Easy £25.00 instead of £29.50 if you tick 'Add the Gem ID book' when you buy the Chelsea Filter.

Not as detailed, but good guide to gemstones, beautifully illustrated, is Gemstones.

A good light source is essential for using optical gem testers, the fine-focus Pen torch.