Given a metal object (let us say a perfect planner uniform surface) that has been exposed to external environment factors such as sun, wind, rain and others for couple of years.

This object has been changed in a way or another. For example, the surface which was perfectly smooth should have been damaged a bit. Those changes may not be visible to the naked eye (or maybe but let us assume that it is not).


Hypothetically, the damaged (changed) surface should not be uniform anymore. For example, the external environment factors will not affect each region of the surface in the exactly same manner.


Given that the previous assumption is true, and using a special camera (non visible; such as infrared, ultraviolet or any other spectrum range), the goal is to get a unique map for that surface that is robust even if the shot was taken from different angle or distances.

More clarification: The surface at manufacturing moment was smooth and uniform. It is simple metal surface that if it was captured by any type of cameras, the result will be uniform (you can not tell which part is which. For example:

enter image description here

After the external environmental factors have affected the surface, I am guessing that the the surface optical response to some spectrum range could be like:

enter image description here


  • Is the mentioned assumption true?
  • What kind of optical response is needed for this task or in other words what type of optical sensor is needed?
  • If all of what were mentioned are not correct or not applicable, what other physical phenomena that I can rely on to detect the mentioned unique map of that surface (any simple clue is much appreciated)

Edit - Clarifications:

  • I do not need topographical map. I need any map of the plate that is unique (so topographical map is an option but not the only one).

  • My goal, for simplicity, is to capture those unique maps for, let us say, 100 pieces of metal and store them in a database and then be able to capture a unique map of anyone of them and compare it to the database and know which one is it (note: the period between the first and second capture is less than day and maybe few hours. So, I am assuming that during this period no noticeable change will occur).

  • Microscope is not an option, the images are captured 1-2 meters far from the piece of metal.

  • $\begingroup$ Hypothetically, the damaged (changed) surface should not be uniform anymore. For example, the external environment factors will not affect each region of the surface in the exactly same manner. It will simply depend on how uniform/isotropic the 'treatment' will be. Artificial ageing in a laboratory would yield a uniform result. Ageing in natural conditions probably not because of non-uniform distribution of wind, rain, sunshine and other factors. $\endgroup$
    – Gert
    Sep 1, 2019 at 14:45
  • $\begingroup$ @Gert thanks for confirmation the assumption! $\endgroup$ Sep 1, 2019 at 15:11
  • $\begingroup$ It may also help to know what you intend to do with this information. If your sole job is to determine that two piece of metal are, indeed, different, that's one thing. If you want to recognize the same piece of metal later, after it is held in a controlled environment, that's another. If you want to recognize the same piece of metal after it has worn further, that's another. If you want to see if an object came from a particular environment, that's another. If you want to see if it changed environments... you see how many different problems there may be here. $\endgroup$
    – Cort Ammon
    Sep 1, 2019 at 15:58
  • $\begingroup$ Looks like your 2nd picture is simply that of a galvanized metal plate. Don't know what the purpose is here, but if you simply want accurate topographical maps of the plate before and after weathering, you could use an optical profilometer to characterize the surfaces. $\endgroup$
    – user93237
    Sep 1, 2019 at 16:01
  • $\begingroup$ Thank you very much for your comments. I have edit my question with some clarifications. $\endgroup$ Sep 2, 2019 at 7:35

1 Answer 1


Exposure to a mildly corrosive environment will indeed etch into that surface a pattern of chemical attack which will be random and hence unique for every part. The amount of attack varies from one metal composition to another.

That surface can then be cleaned by a variety of methods to remove the adherent corrosion products and reveal the microtexture of the metal underneath.

That texture can then be digitally imaged in a device called a metallographic microscope at a convenient magnification level.

That image can them be contrast-enhanced or otherwise digitally processed to enhance the texture.

Finally, there are programs called machine vision apps which are used to analyze the resulting image and quantify the etching pattern on it in ways which allow quantitative comparisons between different images.

  • $\begingroup$ Thank you very much for your answer! metallographic seems what I am looking for. However, microscope is not an option since I am capturing the image 1-2 meters away from the piece of metal. However, thanks for the hint. I am going to search in this area. $\endgroup$ Sep 2, 2019 at 7:36
  • $\begingroup$ so use a telescope instead. you can buy ones that focus down to 1 to 2 meters. $\endgroup$ Sep 2, 2019 at 16:46

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