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Colour Change Garnet Identification


#1

Hi,

I sell gems via auctions online. I am running into an issue with one of my lots in terms of the auction house agreeing to post it as they don’t believe that the lot is colour change garnet.

I have tested it and given them the RI and explained that it is monochroic under a polariscope. They still want an expert opinion.

I am not quite sure how to proceed as the value is probably only £150 for the lot. It is 5carats of smalls, 1.5-3mm and the colour change is not great in my opinion.

I bought them in Tanzania a few years back and I know the dealers know their stuff. Unfortunately, none of that seems to matter.

To get a stone certified would cost about £60 and I don’t know if that would cover the lot. It doesn’t seem financially viable to do this.

Any advice on this would be appreciated. I can upload pictures and give specifics if anyone needs them.

Thanks in advance.

Nicholas


#2

I assume that you have presented data and photos that clearly represent the color change under different types of light.

If you have done that then you are subject to the rules of their site and their opinions. It’s their website and it is their call about listing the material. If they have listed a lot of color-change gems they have probably encountered situations in the past where the expectations and knowledge of the buyer and seller are not the same.

Getting a certification will enable you to A) list the item according to their rules, B) give the buyer confidence that they are buying good and accurately described material, C) give you a good feeling that you have sold fairly, D) allow you to know that you were “right” in your identification of this material, and E) possibly receive a higher price because of the confidence that the certification will provide to the buyer.

If you don’t want to pay for the certification you can still sell the material in other venues.

I have paid good money for color-change stones to multiple online sellers and have not felt that their photos were representative after receiving the material. If you don’t fear the loss of £60 for certification then I would not fear sending you my money.


#3

Hi Nicholas I did a Gem A project for my Diploma in regard to colour change see attached, this is a slide from my power point presentation it explains that there is a difference between colour change and shift in colour. to be determined as a colour change gem it should move from 1 coloured to another on the colour wheel by at least 20 degrees if it does not then it would be classed as a shift in colour and not a colour change gem. hope this gives you some indication


#4

Thank you for your replies. The material is definitely colour change but that information is very useful to know as some of the spinel I own does show colour shifts from purple to pink. Judging by this information it may be colour change material.

In terms of getting the material certified, do you send a whole parcel of smalls, or simply one or two stones to show that it is cc garnet?

I will probably send it to IGI as they seem to be the nearest and recognised. Unfortunately the IGS is not recognised by Catawiki auctions.

In terms of the data I presented, the pictures for incandescent light are not the best to be fair. I was using a xenon bulb in a maglight torch. I did actually suggest to them that I would sell them as green garnet only as the colour change is not as pronounced in the UK as it was in Tanzania.

I gave them the RI values of a few stones as follows:

1.768, 1.765, 1.771, 1.772.

I also explained that they are singly refracting under the polariscope. Some did show ADR, but upon adjustment they were fine.

I was told that garnets “often give confusing results in a polariscope”.

The above pictures show the stones under the torchlight previously described and under daylight bulbs.

In terms of value, I purchased these as rough for $100. I am estimating a value of £150. Is that an accurate estimate?

Again, thank you for your replies. I am learning slowly.

Regards

Nicholas