10x -- Zinc metal in the form of powder laying on a glass slide.

50x – A magnified view of the preceding image of Zinc powder, indicating that it individual grains are extremely tiny. Individual grains measure no larger than 0.001” and are invisible to the unaided eye.

10x -- The above zinc powder dissolved in 1 drop HNO3 and 2 drops H2O and heated to dry on the glass slide.A semi-milky white semi-dry solution with no specific crystal structure

Because zinc dissolves in concentrated HCl the following image shows what the crystal appears like when near dry.

40x – Zinc that has been dissolved in HCl and heated till these super-saturation crystals begin forming on the perimeter of solution.
These crystals quickly re-dissolve if more heat is not applied.

10x – Placed 3 drops of water on this dried zinc + HNO3 + H2O white mass and heated. The white mass began to break-up into smaller sections and would not dissolve.

10x – Inserted a couple KI crystals (right of center), in the dried but re-wetted with water which quickly turned whiter than the surrounding zinc mass.

40x – A magnified view of where the KI crystals were inserted.
The pinkish color is reflected light from my hand on the focus know.
Even when this mass came to dry there was no further reaction of the KI.

10x – In another dissolved zinc solution (1 drop HNO3 and 2 drops H2O) and heated only enough to make sure all the zinc powder was dissolved, but no solution drying began 3 more drops of water was added.
A couple KI crystals were inserted into the solution and no reaction was seen other than a slight yellow solution that I could not capture for an image.
After several minutes and no KI reaction the slide was gently heated and soon the typical violent reaction of Iodine and Nitric acid began.
The above photomicrograph is at the tail end of the reaction, which happens within a few seconds.
By the time I was able to focus and capture this image the reaction had stopped leaving the typical mass of black (reduced) Iodine crystals, which may or may not be contaminated with zinc.

Because zinc easily dissolves in concentrated HCl another test was conducted to see what might happen when KI was placed within such a solution.

30x – Concentrated HCl still dissolving the tiny K2Cr2O7 crystal near center that are bright white due to intense lighting.
The bluish white to clear crystals surrounding the gathered potassium dichromate have definite structure, but I would not use this data as conclusive because the K2Cr2O7 produced no precipitant.

10x – In another identical (as the original) solution a crystal of potassium dichromate (K2Cr2O7) was inserted. There was no immediate precipitation and the crystal began to dissolve.

10x – When the K2Cr2O7 crystal dissolved a gentle heat was applied to the underside of glass slide. After a minute or so this reddish-brown coagulation formed in the crystal had dissolved.

15x – A slightly magnified view of the K2Cr2O7 dissolved crystal, several minutes after the previous image was captured begins to solidify around the edges and became semi-clear in the center.
Even though this is somewhat peculiar to zinc I would not use this as any type of confirmation that Zn is present.
Precipitants are what I look for to allow me to make informed deductions regarding what type of metal or metals may be present in solution.

Although Zinc dissolves easily in concentrated HCl— potassium dichromate does not precipitate anything and is not a reliable reagent for determining zinc.

15x – In another solution exactly the same as original (1 drop HNO3 and 2 drops H2O) a single NaCl crystal was inserted. No precipitation occurred, but after heating the super saturated solution began forming this crystalline structure. Obviously, NaCl is not an agent that can be used to decidedly indicate the presence of Zn in a HNO3 solution.

15x – A toothpick tip was inserted into the original HNO3 solution of dissolved zinc and was ignited. No metal formed.

15x – Because no metal was visible the toothpick tip was reignited and still no metal.

15x – The toothpick tip was ignited again, although no metal was visible the burnt wood had become snow white with a brownish tip.

40x – A magnified view of the preceding image.
Obviously zinc does not reduce by this method.

Over-all conclusion is that Zn in a HNO3 + H2O solution fails to provide reliable data with the reagents used.
The best test is the drying of solution and then adding water and heat. If the white dried mass does not re-dissolve then I would consider the potential of zinc being present. However, other elements will also behave similarly under same conditions.
Therefore, it would seem prudent to use other chemicals to produce desirable results.

Pb + Zn

Lead and powdered Zinc fused together on plaster tablet.

20x – The powdered 99.9+% pure Zinc and the 99.9+% pure Lead button fused into this single mass.Although these two metals often share the same mineral matrix it appears that they do not like to intimately embrace each other in a melted format.

20x – The Zn+Pb metal bead (upper left corner and out of focus) was subjected to a solution of 1 drop of HNO3 and 2 drops of H2O.This solution was heated gently and as the amount of solution vaporized the remaining solution became super saturated producing these white to clear crystals.

50x – An attempt to capture the semi-transparent crystals growing on the Zn+Pb metal bead as a result of the solution becoming super-saturated.
The slight amount of pink color is due to reflected light off my hand while trying to get a decent focus to capture this digital image.
The metal is grainy indicating that this is not pure Lead, which is another way of ascertaining an alloyed metal.

15x – The same preceding solution just prior to becoming almost dry, which produced these off-white crystals on the metal button.
Subdued lighting was used to be able to see what appears to be primarily Lead Nitrates pacifying the metal surface.
Zinc contamination of the lead nitrates seems present, because the Lead nitrate crystals would be whiter if no impurity was present.

10x – The metal button has been removed. The solution is almost dry, with super saturation crystals forming.
The white crystals in center appear to be some form of zinc.

40x – After a few minutes this K2Cr2O7 became elongated in height
Normally, in a Lead nitrate solution potassium dichromate will precipitate yellow-orange crystals, which sort of attempted, but would not finish.

17x – Same image as above, but less magnification to be able to see a larger portion of the solution that is beginning to dry.
The white crystals towards the center might be some form of zinc, whereas the crystals along the perimeter appear to be Lead nitrates with Zn contamination.

40x – After about 10 minutes another magnified view of the large peculiar shaped K2Cr2O7 indicating obvious changes. It is always best to set aside each test and let time work its wonders versus using the same solution for more tests. However, and having said this I constantly also need to see what may happen with additions or water, more heat or as indicated in the next paragraph.

Placed another potassium dichromate crystal near the one pictured after another drop of water was added to this solution. There was no significant change. Repeated again with another drop of water and still no appreciable change to how the potassium dichromate formed. Therefore, it appears that this kind of shape may well be indicative of the presence of Zinc with Lead.
Inside this apparently hollow shape are orange needle-like crystals, which appear to be Lead Chromate. Unfortunately I could not get good enough resolution to capture.

40x – In another identical solution as the original these 3 NaCl crystals were inserted. I meant to only apply one, but the wetted toothpick tip collected 3 instead of just one.
There was an immediate precipitation of the growing Cl crystals, which resemble PbCl.

40x – After a few minutes these 3 NaCl crystals began growing towards the perimeter of solution.

15x – A reduced image showing the 3 sodium chloride (table salt without any trace Iodine) crystals radiating towards the solution perimeter.

35x – In another identical solution, but with 2 additional drops of water and only 1 NaCl crystal the more typical Lead Chloride crystals with feather appearence began almost instantly growing.

35x – About minute after the insertion of this single NaCl crystal the reaction began to subside.

40x – This magnified view of the 2 preceding images and the salt crystal dissolved – shows the distorted feather type crystals suggesting that the Lead Chloride crystals are contaminated with Zinc.

35x –1 drop HNO3 + 2 drops water that was gently heated to digest a little of the ZnPb metal. Then 7 more drops of water added and a single crystal of KI inserted into the solution.
The center area somewhat resembles Lead Iodide crystals (the white dots of reflected light), whereas the rest appears to be severely contaminated (undulation areas). Because only Zn & Pb inhabit the solution a pragmatic assumption that zinc is definitely influencing the structure of this KI precipitation.
If the HNO3 was causing interference problems most likely there would be brown-red formation, which is the typical reaction of KI and nitric acid.

Click Here to watch a 2.73MB video clip of this KI insertion. Notice that when the KI on the toothpick tip touches the solution there is an instant precipitation, which indicates the need for further dilution.

20x – In the same solution as preceding image but 2 more drops of water was added for additional dilution to obtain visual effects of dilution.
This additional dilution certainly allows better resolution of the lead iodide crystals (shinny spots).
The yellow is full of these tiny PbI crystals, but are not visible at this magnification.
Click Here to watch a 1.85MB video of this particular KI reaction to the further diluted Zn and Pb solution.

10x – This toothpick tip was dipped into the original HNO3 solution and ignited. No obvious metal was reduced. There is some metal beads on the blackish area, but these are very small and I could not obtain a decent focused image. Apparently, the Lead was volatilized along with the zinc, leaving this yellowish tip that no matter how many times it was ignited failed to produce metal beads.