We are going to look at the Chelsea colour filter
They were initially devised in the 1930s as a test for emeralds, to aid in their identification
and separate emeralds from simulants such as glass or other green gems.
And they were for a while capable and recommended for that purpose, but the emerald world changed,
they became less effective and if that's all they had done they probably would no longer
be produced.
But the filters were subsequently found to be capable of distinguishing gemstones other
than emeralds and so remain not only in production but a very useful gemmologists tools.
Now it seems if you want to start an argument with or amongst gemmologists start a conversation
about emeralds, and that's not what we are making this video to do, it was about how
to use this tool.
But I think we need to look at the arguments surrounding emeralds to understand why this
filter was capable of detecting emeralds but no longer is.
The first reason it became less effective was lab grown synthetic emeralds became available,
but it was still useful as once you had sorted other simulants from emerald you just needed
to check for any indication of synthesis.
doing a bit of research I just watched a YouTube video about Zambian emeralds and in the comments
below was a member saying that its ironic the video presenter is English and the English
lead by the gemmological association of great Britain only recognise emeralds that originate
from Columbia and then there is actually a reply from the chairman of gem-a questioning
this and saying gem-a is hardly discriminatory and they and their course notes recognise
emeralds from many countries and have published articles about mines in Zimbabwe since the
1950s.
But there does seem to be a common belief in internet threads and posts that that the
GIA and Gem-a disagree about what constitutes an emerald and so I started to try and find
out the origins behind this story.
One things for sure the more articles you read about what is an emerald, what are its
defining characteristics the more confused you get especially on the internet when you
find things like yellow emerald for sale so I started to look at text books.
Looking at a text book of precious stones from 1918 it simply defines emerald as the
common name for green beryl and that blue beryl is commonly called aquamarine, brilliantly
clear and simple.
But then In the 1945 first edition of the retail jewellers handbook it publishes a list
of standard gem descriptions with both correct & incorrect trade names approved by jewellery
associations from around the world.
And within that list they separate beryl into 5 correct trade names in total, on this list
bright green is called emerald and just green is called beryl.
It's the first published separation of green beryl & emerald I can find, there are no doubt
others but it's the first I stumbled across.
But they describe emerald at more length in other sections and there is no mention of
this separation or when bright green becomes just green.
And that's just one of the arguments about emeralds should there be a certain saturation
of colour at which green beryl becomes classified as emerald or not and then obviously you could
argue endlessly about where the line should be drawn.
The biggest argument and cause for confusion appears to centre on the chemical element
responsible for making emeralds green.
It is also the reason this filter became ineffective for testing emeralds
In the early 1960's, large deposits of beryl were discovered in Brazil.
It seems until this time much of the world's emerald supply was originating from Colombia
and its color came from traces of primarily chromium.
At this time many text books had already been published stating that emeralds contained
chromium and the Chelsea color filter functioned on these emeralds because of the chromium.
So much to the frustration of the miners and dealers, the industry refused to consider
the Brazilian material as emerald because its color was caused primarily by vanadium
and lacked the chromium content of other green beryl.
Then In 1963, the GIA laboratory issued its first lab report identifying this vanadium
colored green beryl as emerald.
And in their curriculum, began to teach that vanadium beryl is emerald.
This decision 50 years ago would have had far reaching financial consequences, there
would have been winners and losers not least the Brazilians.
It would have certainly been a blow for the producers and suppliers of the Chelsea color
filter as it could not detect the vanadium gems.
And that was the main reason it became ineffective as a test for emeralds because, although it
can still separate chromium from vanadium Beryl it cannot positively identify vanadium
beryl which was not being sold as emerald.
I have no information about the GIAs decision about vanadium beryl being disputed then or
now and it was 50 years ago so if anyone has any information or stories from that time
let everyone know in the comments below.
It would be interesting to know how people felt at the time as it's still a little unclear
now.
Did the world accept the decision, disagree or just try to ignore it?
The only reasons I can find that would make people believe this decision is or was disputed
is more recent & current text.
Current GIA information does seem a little more inclusive by saying emeralds are beryl
with a varying presence of chromium, vanadium and iron.
Whereas gem-a text published in 2008 states the green color of emerald is caused by traces
of chromium although vanadium may also be present in some stones, now if that were the
case I think the Chelsea filter would generally still work as it did pre 1963 GIA decision
on vanadium beryl.
And gem-a still teach its use, and their text on it or their instruction for its use do
not mention vanadium colored beryl.
There is however a sentence on both saying new varieties of gemstone may differ, but
50 years old is not new?
So it may be my misinterpretation and others of their text but the two do appear to differ
in opinion not on country of origin of emeralds but chromium content.
So anyway in the comments below any information about this seemingly conflicting view about
chromium being a requirement would probably be a more productive and helpful conversation
to have than arguments about the color saturation separation of green beryl and emerald.
So now let's look at what this filter can do
You can use it to test individual stones but it's also brilliant at checking larger quantities
of stones rapidly to spot odd ones out.
If we compare aquamarine and blue topaz they look very similar in color to the naked eye
but through the filter they look different.
You place the stone being tested on a white background like a piece of white paper, and
then shine a bright light source on it.
Then you look at it through the filter holding the filter close to your eye.
You can see the aquamarine looks greenish blue but the topaz is yellow- colorless
Now let's compare ruby and garnet
The ruby is bright red but the garnet dark
red