I think it depends on what the wedges are used for. For example,
silver-based step wedges are not truly accurate for calibrating
internegatives because the gray in color slides are not the same as the gray
of silver. Although KODAK does sell wedges made from chrome materials, they
recommend using the silver step wedges probably because they are inexpensive
and don't fade. I believe this is under the assumption that a slight
imbalance in internegative can be corrected during printing as long as it is
not grossly crossover.
For most of us, I think silver-based wedges are fine especially if we are
making large silver negatives from smaller silver negatives. The materials
actually match.
>>>> I too have heard about the use of pigmented gelatin for the manufacture
of
step wedges, but am not sure if this method is currently in use. I seem
to remember that the calibrated density standards sold by Edmund
Scientific use metalized glass slides. >>
I happen to receive a catalog from them today, so I checked it out. They have
a large (8x10") gray scale target on .2mm mylar, the cost is $75.00. They
also have an EIA Gray Scale Pattern Scale, which is on glass, and with
precise tolerance. The cost is $332.00.
Comparing the prices, I think KODAK's photographic step tablet and Stouffer
step wedges are film based.