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 Post subject: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 2:42 pm 
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Having recently bought a Refratometer, I'm still having trouble mastering it.
I know it takes time and practice, but I seem to be getting nowhere.
There is no definite deviding line. The best I can hope for is a slight shading to the top of the index list and the remainder is bright.
Today I used a flat sided agate that I had recently slabbed and just a small spot of index fluid. Still the light shading, but as I moved the stone I saw what appeared to be a bubble on the index list. And this moved as I moved the stone. But no definitive line.
And no, I did not use a large amount of fluid. Just enough to cover a pin head.
Any advice how to sort this out would be appreciated.


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 2:59 pm 
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What sort of light source are you using?
Are you using a polarized filter?
Are you using a sodium (583nm) light source or full spectrum?

I always recommend starting with some known gems....which are on the larger side and well polished.

Faceted amethyst
Faceted Synthetic flame fusion spinel and ruby.
Faceted fluorite

Since you know the refractive index you are looking for, it is easier to recognize exactly what you are seeing.

Have you read our page on the refractometer on the GemologyProject?
http://www.gemologyproject.com/wiki/ind ... ractometer


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 4:09 pm 
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The light source Is included in the machine.
Yes, I'm using a polarizer filter.
Not sure about the sodium light, but the light is yellow.
I will be taking your advice on using an Amethyst.
Yes, I've already seen the YouTube on your suggested page and will be reading the rest of the page as soon as I can.

I do wonder, as I only paid about £55 for the refractometer new on EBay, could it be that it's too cheap a machine for giving good readings?


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 5:05 pm 
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For 55 pounds you can certainly get a refractometer that looks like a refractometer but hardly one that works as a refractometer ! :?


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 7:48 pm 
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That's a pity :(
But I did check out the feedback and also checked out reviews for it and they spoke well of it.
But I guess that's life.


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 01, 2015 8:16 pm 
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that's about what mine cost, and it works fine. Try moving your eye up and down as you look at the graph. It is really a change in the amount of gray rather than a "line". the boundary between two different shades of gray.


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 Post subject: Re: Problem with my refractometer
PostPosted: Mon Feb 02, 2015 2:12 pm 
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Well, I've tried it again and it's really hard to differentiate between the grey and the clear.
I don't think its a very accurate way of confirming your type of stone.


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 Post subject: Re: Problem with my refractometer
PostPosted: Mon Feb 02, 2015 4:08 pm 
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A good refractometer is quite sharp and reliable. If you buy an excellent instrument the first time, it will last a lifetime.
I'm going to redundantly suggest (yet again)
http://www.gemproducts.com/refractometer.html

I back mine up to a polariscope; I don't use the maglight.


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 Post subject: Re: Problem with my refractometer
PostPosted: Mon Feb 02, 2015 6:04 pm 
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I have barbs back on this one, you get what you pay for. With those china cheep instruments, sometimes they work, sometimes not. It is a buyer beware! Remember you are dabbling in non destructive scientific testing, the equipment used to get reliable results MUST be scientific quality to obtain this.

I have not used the refractomiter Barb suggest but if she is recommending it, then its more than likely worth it. I my self prefer the GIA Duplex 2.

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 Post subject: Re: Problem with my refractometer
PostPosted: Mon Feb 02, 2015 6:14 pm 
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This is about the price a good new material is supposed to cost.

Depending on where you live, you have the english catalogue too :

http://www.gem-a.com/shop.aspx

And I agree, with a proper refractometer the line is quite sharp and neat, if the facet is flat and within reading range. No fuzzy difference between two gray zones !

Too cheap is always too expensive !


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 Post subject: Re: Problem with my refractometer
PostPosted: Tue Feb 03, 2015 2:06 am 
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What my dad neglects to say is that, while he didn't pay much for the refractometer, he got a decent one which had been lightly used in a very favorable eBay auction. It wasn't that price new by any means. And it's not that hard to see the line at all in ours.

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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 08, 2015 12:59 am 
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There are many opinions about refractometers, and here is mine.

I have just returned from Tucson and the going price for a “top of the line” refractometer is about $1,000. That is simply ridiculous.

A refractometer is a very simple instrument. It either works or it doesn’t work, or the operator is unskilled. Above, Brabra has shown how one can test its calibration.

Today, I and my peers believe no one should ever have to pay more than $200 to get a good one, unless you want to pay extra for the name printed on it. There is indeed often a difference between what an instrument sells for and what it is worth.

Now, if you might willing to spend a day or a weekend in Monterey, CA, to see the aquarium or golf, while you are there, for $1,000, I can teach you more than you want to learn about Gem ID, and even throw in a free refractometer. (But first have to pass my test) :D :D


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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 08, 2015 3:35 am 
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Hi,

If the surface of the slab that you want to mesure is very rough, than you will not see a good line. Try first this large 0.5 carats up good polished faceted gems.

Good luck,
Timur

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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Feb 08, 2015 6:10 am 
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I forgot to tell you: never put the sample on the refractometer with a tweezer you can scratch the table and line will not be seen well. Use you hand even for very small stones it will make your refractometer last much longer.

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 Post subject: Re: Problem with my refractometer
PostPosted: Sun Mar 22, 2015 6:18 pm 
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I bought a cheap Chinese refractometer with built in light source and find that with care it works quite well. The problem area seems to be the light source, it is fitted with a full spectrum LED behind a filter, I am toying with the idea of changing the full spectrum LED for a sodium colour one. Not as good as the correct sodium light but on the other hand much better than the filter (see the spectrum in "Gems"). It may be that because I am working with fairly large faceted pieces it is easier, but I intend to try it with cabochons soon. I also think that a mat surface will not give a good reading.


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