Question for experts!

[JLW05]

I purchased an inexpensive diamond tester and it arrived today. At first, none of my diamonds, even my GIA certified ones were testing as diamonds but after carefully cleaning my pieces and reading the instruction manual quite carefully, the tester worked. I not only tested my diamonds but my small collection of colored stones as well as they served as my "control" group. I got one strange reading however. I have a very old ring with 3 very small untreated rubies. All 3 rubies tested as diamonds. I tested them over and over but kept getting the same results. I also have another inexpensive ruby ring and the rubies are Be filled. These rubies did not test as diamonds. Is this a glitch in the tester or does it have something to do with the properties of untreated rubies? My other colored stones all tested negative.

 

[chrono]

Not all testers are created equally; the Presidium is known to be "flaky". It is best for diamonds only, not coloured stones. As you've also experienced, dirt changes the conductivity, and might give you incorrect results.

 

[LD]

If I recall the next step along from the diamond reading is glass isn't it? If that's the case, is it possible that the "ruby" is actually glass hence the reading?

 

[JLW05]

I actually did a bit of research after I posted. I am not much of a science person but the reason the ruby tested positive is a diamond tester actually measures thermal conductivity. A diamond has a very high level of thermal conductivity (although synthetic moissanite has the same level of thermal conductivity and can fool diamond testers). However, rubies also have a high-ish level of thermal conductivity. If one owns (as I do) an inexpensive diamond tester, that tester will beep when it senses the thermal conductivity but it does not give a specific measurement as would an expensive diamond tester. A diamond would measure much higher for thermal conductivity than a ruby.