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Some
glass applications call for a roughend surface, by etching or sandblasting.
The surface of the
glass can be chemically treated to produce a roughened,
or frosted appearance, much like sandblasting. This surface
preparation can be useful for holding a coating on the glass
surface. Hydrofluoric acid or ammonium bifluoride are the most common etching agents. Etching borosilicate glass is more difficult than soft glass. Our experience with getting just the right amount of etching is illustrated below. |
The following
photos show a series of scanning electron micrographs of the glass
surface after treatment. The three samples are shown with scale marks
at 10 and 1 micron, respectively:
The above results were revealing.
The process involves the formation of silicon fluoride crystals on
the surface of the glass. SiF is water soluble, and it is the reverse
image of the angular crystal structure left behind after rinsing
in water that produces a rougher surface, more scattering of light and less specular
reflection.
An interesting feature was revealed in the micrograph of the over-etched
sample. The “highs” of the previous sample have themselves
been etched down, having the effect of flattening out the surface,
resulting in less light scattered and a glossier surface. You can imagine how much this drove us nuts.
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