> This reminds me that I read somewhere, about 10 years ago, that step wedges
> were made by some carbon process, in part because of the nature of the
> pigment that could be employed. It was more desirable than a silver image
> for some purposes. Does anyone know how step wedges are made nowadays?
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 don't have a catalog handy to
check though.
My guess is that like most reference standards, there are several levels
of quality depending on the degree of precision and accuracy you need.
The inexpensive step wedges are almost certainly film based. Standards
laboratory quality artifacts probably are not. For the alt-processes I
doubt that "standards" quality step wedges are needed.
According to the NIST Calibration Services Users Guide, the technical
contact for Spectrophotometric Measurements is:
P. Yvonne Barnes
Tel. 301-975-2345
I don't seem to have her e-mail address handy, but you can look it up on
our web site at http://www.nist.gov if interested. Unfortunately this
division is located in Gaithersburg, MA and I work in Boulder, CO or I
would go ask for you.
Some references given in the SP250 are:
Measurement Assurance Program - Transmittance Standards for
Spectrophotometric Linearity Testing: Preparation and Calibration,
K.L. Eckerle, V.R. Weidner, J.J. Hsia, and K. Kafadar, Journal of
Research, National Bureau of Standards, (U.S.), 88(1), 25 (1983)
Basic Considerations of Densitometer Adjustment and Calibration,
R.E. Swing, National Bureau of Standards, Report 10970, Dec. 1972
Permanence of Glass Standards of Spectral Transmittance,
K.S. Gibson and M.A. Belknap, Journal of Research, National Bureau of
Standards., 44, 463, May 1950
There are more listed, but these seemed to be the most relevant. Yvonne
I'm sure can refine this list, and give you better information.
Hope this helps.
- Wayde
(allen@boulder.nist.gov)