40x – Powdered (-200 mesh & 99.99% purity) Rhenium metal, that I cannot get a better clarified image than at this magnification.

10x – The Rhenium powder was digested quickly in 1 drop HNO3 and 1 drop H2O.
The metal dissolved quickly when a little heat was applied.
When the solution was dry a blackish ring formed at perimeter of the solution area.
The dried Re solution began to re-liquefy, which this image illustrates.
The solution is a blue green.
The vapor fumes had an odd odor.

10x – This image was captured a few moments after the previous image.
Add water the blue green becomes blue
Nitric & water almost instantly re-dissolves the blue green dried Re and the solution becomes clear.

10x – A single crystal of potassium dichromate is inserted into this solution of 1 drop HNO3 & 1 drop H2O that dissolved some Re powdered metal.
No precipitant formed.

10x – The dried solution of the previous image with the K2Cr2O7.
Obviously, potassium dichromate is not a reagent to use to determine if Re is present in a nitric acid solution.

10x – The Rhenium metal powder dissolved in 1 drop of HNO3.
The reaction was immediate and solution turned an instant green.
When a little heat was applied to underside of glass slide the remaining metal dissolved quickly.
When the drop of HNO3 was placed upon the Re metal powder copious amounts of red nitrous oxide fumes instantaneously.
When more heat was applied some metal was reduced.

30x – A magnified view of the preceding image, which better illustrates the reduced metal.
The squiggly area must be caused by the reduced metal running around as the solution dried.
There is a brilliant, beautiful red colored mirror-like coating on the glass slide when the slide is held at an oblique angle.
When the glass slide is removed from the white microscope stage the coloration on the slide becomes a beautiful indigo blue instead of the greenish
However, when this solution has sat several minutes the beautiful blue color is no longer visible. Apparently, the non-reduced portion absorbs moisture from room air and becomes a dirty green.

30x – A magnified view of the preceding image, which better illustrates the reduced metal.
The squiggly area must be caused by the reduced metal running around as the solution dried.
There is a brilliant, beautiful red colored mirror-like coating on the glass slide when the slide is held at an oblique angle.
When the glass slide is removed from the white microscope stage the coloration on the slide becomes a beautiful indigo blue instead of the greenish
However, when this solution has sat several minutes the beautiful blue color is no longer visible. Apparently, the non-reduced portion absorbs moisture from room air and becomes a dirty green.

10x – Same as previous 3 images, but with water added, which does not dissolve the red metal areas and has this beautiful blue color that has dissolved the unreduced areas.

10x – Same photomicrograph as preceding image with the water, but now the water has dissolved all that would dissolve leaving what appears to be reduced metal.

A single drop of HNO3 was placed upon this reddish looking reduced metal and it almost which instantly dissolved. Then, a Potassium Iodide crystal was inserted into the HNO3 solution, which was diluted with 3 drops of water. No precipitant formed.

Note: Ammonium Chloride was inserted into another Re + 1 drop of HNO3 and no precipitant formed.

Note: When heating the glass slide containing only HNO3 & Re powder there is considerable white vapor/fumes, which increase as the solution begins to dry. The solution becomes oily appearing and copious amounts of white fumes/vapors evolve that resembles smoke.

Out of curiosity a few more tests were conducted to confirm these previous microchems. And, after several similar comparative test none were like the above image spectacular results.The next 2 images attempt to illustrate a few of the differences.

15x – This is another example of the Rhenium powder dissolved in 1 drop Nitric and brought to a dry state. This test illustrates that although the circumstances are essentially identical the outcome is somewhat different .
This test on a white background shows a bluish-green dried state, yet when viewed on a black background there is a remarkable color shift as shown in next image.

10x – This black background indicates not only color shifts but what appears to be reduced metal that did not appear on previous image.

Several similar to identical tests were conducted and each continued to produce amazingly different results with some similarities, such as the next image.

40x – This test of Rhenium dissolved in 1 drop of HNO3 produced these greenish needle crystals, which quickly dissolved. Subsequent heating also produced some of the reddish reduced looking metal.

10x – The Re powdered metal and a few crystals of Lead nitrate were dissolved at same time in one drop of HNO3 and 1 drop H2O. Then the solution was slowly brought to dry by heating the underside of glass slide with cigarette lighter flame, which produced this green Re ring formed on the perimeter. Coincidently perimeter ring is similar and seems to be a rather normal circumstance for some elements to form when brought to dry with various contaminating elements.

40x – Magnified view of previous image at about the 10 o’clock position.
No red metal formed no matter how many tries were attempted with varying amounts of Re and Pb. In fact not a lot of the blue or green colors formed, but the green matrix seems to be more concentrated.

10x – This image of a drop of HNO3 has digested some powdered Rhenium metal and a crystal of Oxalic acid was inserted into the solution to form this crystalline mass when the solution became super-saturated due to applied heat.
No precipitation formed.
This mass of heat induced crystals became significantly altered as shown in next image.

10x – When more heat was again applied to the Rhenium powdered metal as shown in previous image a definite reaction occurred as if the Oxalic acid was incompatible with the dissolved Re..
The next image is of the same test, but after a few minutes and more heat applied.

10x – With significantly more heat applied to the previous imaged test red appearing metal manifested. Plus, these bluish colored globs appeared with a semi-metallic appearance, but eventually dissolved by sucking-in moisture from the air.
When water is added there is a very pretty reddish metal reflective mirror like sheen, which only dissolves when HNO3 is added.
Conclusion: Oxalic acid, like all the other prior reagents is not a reliable chemical to indicate the presence of Rhenium in a nitric acid solution.

40x – This new test image depicts these precipitated crystals after several crystals of KI were inserted into a 1 drop HNO3 acid that digested Rhenium powdered metal. These crystals slowly formed, but only after gentle prolonged applied heat to underside of glass slide. These crystal formations changed into what is shown in the next image.

10x – These crystals formed when more heat was applied to the previous imaged (KI) test. These crystals quickly dissolve. Repeated heats continue making these crystals and I was not able to heat enough to cause complete dryness for more than a couple seconds.
Obviously KI is not a reliable reagent to use to determine the presence of Rhenium in a nitric acid solution.

10x – This toothpick was dipped in 1 drop HNO3 & 1 drop H2O that dissolved some Rhenium powdered metal.

40x – A magnified view of the preceding image.
No metal was reduced, but based upon the next test when water is sued with HNO3 to digest the Re the H2O inhibits metal reduction.

10x – This toothpick tip was dipped in 1 drop of HNO3 that had dissolved the Rhenium powder.
Obviously, just with a low magnification there is a significant difference when water is NOT part of the equation.
Notice the blue with white that was not present when water was part of the digestion.
This magnification indicates metal formation, but not clear enough, so the next image better illustrates what this image suggests.

40x – A magnified view of the previous image, which better illustrates the high probability that metals was reduced.

Based upon the number of microchems it appears that Rhenium in a nitric acid solution is best confirmed by color. However, there remains many potential reagents that might produce a decidedly and definite precipitant which confirms the presence of Re in a HNO3 solution.