Revealing etched design on glass for viewing under a microscope

Question

Not strictly related to biology, but I believe your expertise would still be very valuable.

I have a glass "slide" onto which a design has been etched (or perhaps more precisely and coating was applied to the glass and then this coating was etched). It is invisible if you look at the slide straight on, but if I get the angle just right with a light source behind me (e.g. the sky), then I can see the design. I include a photo below to show this.

Are there any tricks or setups I can use so that I can easily get the etched design to be visible under a microscope? I don't need it to be high quality, just visible. Perhaps a different type of light source, coatings, etc.

Answer 1

Since etching is creating microscopic surface height changes my immediate idea is:

1. place point light source at very sharp angle, maybe a laser
2. use dark background, maybe a flocking paper
3. paint the facets black to not let any unneeded light into the glass from the sides

I imagine it will create visible outline of the etching. Maybe shining the light through the edges (and not letting it through the top) will work better. Maybe you can paint the etching white with some chemical (so that the paint fill the carves tightly) and then shine the light through the edges, that might work too.

Another suggestion is to maybe make a sandwich of clear glass + coloured solution + slide and squeeze it (slightly). I imagine it would leave small amount of solution where material was etched. The solution must have very low viscosity I guess.

If you use a coloured solution and cover it not with clear glass but with something bendable (maybe thin plastic or even plastic film) I imagine you can get an outline too since small amounts of solution will be trapped where the sharp height difference is.

I do not know what the etching depth is but if nothing works well there's also interference light tricks that you can explore. The principle is that self-interference of light can reveal the etching because it depends on the optical length.

Answer 2

The simplest way will be to use a coloured solution of some sort - food dye/colouring, indian ink, and pen ink (fountain pen) would all be good candidates. You would probably also want to have a suitable solvent to remove the coloured solution too. The idea would be to flood the slide, then drain off the excess onto tissue. The etched area should retain the dye more than the smooth surface, which should clear almost entirely.

However, the true answer would depend on what sort of microscope you have. If you have one with an adjustable position light-source (e.g. dissecting scope), then you should be able to see this with light at an oblique angle much like you have done above. With a transmission light microscope (upright or inverted) then staining the etched area would be easiest.

Reflected light on a dissecting scope with a dark background should work well too, though you want a uniform light source and an even background for ideal viewing.