can gauge scratch stones?

[Arkteia]

I bought a sliding millimeter gauge with stone tray on ebay. It is very convenient to use, so I decided to take "vitals" of some stones that I have purchased. The first one was my CC garnet (poor guy!). I put him into the tray and measured the diameter. Then I thought, no it is not enough, let me measure the depth! Maybe I shall end up ordering a setting for it from Sally. So I put it on the side and squeezed from both sides...and then it hit me, the gauge is made of some hard metal, it can scratch the garnet! So far I have not seen any scratches on it, but still. My spinel and tourmaline got it lighter anyhow.

So can a gauge scratch a softer stone, like a garnet? And given its use, why make it out of some hard material?

 

[chictomato]

Hi crasu that is an interesting question and I am sorry about your stone. I am pretty much a novice. But my jeweler friend did mention that there is a possibility of scratching the softer stones. Hence he recommend a plastic steel caliper instead. Hopefully more pros will chime in I do wanna know more too!

 

[Lady_Disdain]

It would depend on the alloy and tempering used - steel can range from 4 (common steel) to 7.5 (hardened tool steel). I would imagine a gauge would be made of hardened steel, but not the hardest steel around. So perhaps a 5 or 5.5? However, since the face of the gauge should be pretty well polished, I would think it wouldn''t scratch gems so easily. You might try scratching a piece of glass with it, just to see how easy/hard it would be.

What does worry me is chipping the girdle or crushing the cutlet (when taking depth measurements). Chipping doesn''t depend so much on hardness but on brittleness and can easily happen if the gem is struck just so. Or so says the person who chipped a trillion tourmaline last night, while trying to bezel set it.

 

[Arkteia]

Date: 3/27/2010 9:30:01 AM
Author: Lady_Disdain
It would depend on the alloy and tempering used - steel can range from 4 (common steel) to 7.5 (hardened tool steel). I would imagine a gauge would be made of hardened steel, but not the hardest steel around. So perhaps a 5 or 5.5? However, since the face of the gauge should be pretty well polished, I would think it wouldn''t scratch gems so easily. You might try scratching a piece of glass with it, just to see how easy/hard it would be.

What does worry me is chipping the girdle or crushing the cutlet (when taking depth measurements). Chipping doesn''t depend so much on hardness but on brittleness and can easily happen if the gem is struck just so. Or so says the person who chipped a trillion tourmaline last night, while trying to bezel set it.

I am sorry for the tourmaline. Hopefully the chip was small.

 

[Michael_E]

Date: 3/27/2010 3:55:00 AM
Author:crasru
So can a gauge scratch a softer stone, like a garnet? And given its use, why make it out of some hard material?

Gauges are made of harder materials in order to be durable and provide accuracy over a long term. That said, the best sliding gauge to have is one made from brass and then just use it carefully and store it in a plastic bag. You will need to use it carefully anyway since, as Lady Disdain has mentioned, it is very easy to chip girdles and culets on stones which are more brittle. This doesn''t happen through impacts, but by twisting the stone slightly while it''s being measured. Scratching can also occur if there are any particles of hard materials stuck to the faces of the gauge, so make sure that they are very clean before use. One other area where scratching can occur is by placing the gem table down on a flat surface and then sliding it around. There are lots of places in the country where dust in the air can be partially composed of hard particles, or you may have some hard particles laying on that surface from previous measuring attempts or from emptying a parcel paper where stones were allowed to move against each other. Even dust from some types of paper can have abrasive particles in it. It doesn''t take much to create small scratches in some stones, so always make sure that you lay them down on a clean surface, I usually lay them down on a piece of a white plastic cutting board, since I know it''s clean and they are easy to see.

 

[zeolite]

Date: 3/27/2010 9:30:01 AM
Author: Lady_Disdain
It would depend on the alloy and tempering used - steel can range from 4 (common steel) to 7.5 (hardened tool steel). I would imagine a gauge would be made of hardened steel, but not the hardest steel around. So perhaps a 5 or 5.5? However, since the face of the gauge should be pretty well polished, I would think it wouldn''t scratch gems so easily. You might try scratching a piece of glass with it, just to see how easy/hard it would be.

What does worry me is chipping the girdle or crushing the cutlet (when taking depth measurements). Chipping doesn''t depend so much on hardness but on brittleness and can easily happen if the gem is struck just so. Or so says the person who chipped a trillion tourmaline last night, while trying to bezel set it.

http://www.sciencetoolbox.com/articles/Mohs-Hardness-Scale.html

Look at this link, toward the bottom, for hardness of common materials. I''ve never seen a steel millimeter caliper. All I''ve seen are brass. At hardness 3.5, it is softer than a very soft gem material, opal, and even softer than apatite. That is probably why brass was chosen for the gauge.

As you say though, chipping is a very real problem. I use a plastic dial caliper when I''m measuring depth (table to very delicate and sharp pointed culet).

 

[T L]

What about digital gauges, aren''t the calipers on those made of steel?

 

[Michael_E]

Date: 3/27/2010 1:05:27 PM
Author: tourmaline_lover
What about digital gauges, aren''t the calipers on those made of steel?

Yes they are. But they are made for diamond measurements and it is a lot harder to chip a diamond than a garnet. If you are measuring a stone which has rounded girdle facets, then you''ll probably be O.K. with any gauge. If you are measuring a precision cut gem, with very sharp girdle break facets, then you need to be VERY careful with any gauge. A little twist between the stone and caliper faces is often enough to pop the edge. I wish more cutters would "break", (a metal working term), the edges of their stones when polishing. This is a slight bevel at the break facets that is very hard to see, but it trims the sharp edge just enough to make it MUCH more resistant to chipping.

 

[Barrett]

I use a poly hard plastic guage..never thought of any made of steel..my guess is if it is steel it''s for something other than gems..all the gem ones are brass or some type of hard plastic

 

[Lady_Disdain]

Date: 3/30/2010 12:57:05 AM
Author: amethystguy
I use a poly hard plastic guage..never thought of any made of steel..my guess is if it is steel it''s for something other than gems..all the gem ones are brass or some type of hard plastic

I have one made of what I believe is steel - whatever metal it is, it is quite hard. I know it is not for gems (and I don''t use it for gems - most of the time) since I, ahem, kindly rescued it from my father''s treasured tools (aka, stole it right under his eyes

).