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by Ron Joseph
December, 2005
Fed-Std-595 vs. L*, a*b* Color Coordinates
Q. I work at Universal Avionics as a supplier Quality Engineer. We manufacture
many aviation electronics including the "Black Box", FMS (Flight Management
Systems) and other various cockpit display devices. One of the specifications
that we need to maintain is no contrast between faceplates over time. With this
being said, our standard that we send to our supply base currently calls out
L a*b* color coordinates and this is sometimes confusing for them. I would like
to move to a FED-STD call-out, but am hesitant on doing so for the following
reasons.
- Is there a tolerance range on the colors? If so, how tight and what units?
- What happens when the FED-STD colors are changed and we will be receiving
parts that meet the FED-STD color, but do not match parts from years past?
If you need any more details, let me know. We are also struggling with a
paint contractor and non-reflective surface paint (Spectraflect) being too "clumpy"
and I think that the propellant settings may be the cause.
Finally, are you planning to run any more classes as mentioned on this website?
Thanks-
A. The Fed Std. 595 does not give you color tolerances as these are values
that you must provide to your vendors. You have various options:
- You can standardize the colors yourself and send color chips to your vendors.
These must be carefully prepared and you will need to insure that each color
chip falls into your own specified tolerance.
- You can specify the L*, a* b* values but you must also provide a Delta E
tolerance. To do this you can get color chips that are slightly different
from one another yet fall into your acceptable tolerance. By measuring the
Delta E between them you can establish a quantitative measurement for what
is or is not acceptable.
- Perceptible color is VERY dependant on gloss; therefore, you will need to
specify the gloss and its tolerance.
- Method of paint application is definitely a factor in the perceptible color
of a coating. If your contractor is having difficulties in matching your color,
it can be caused by many variables, such as atomizing air pressure, fluid
pressure, mixing, gun-target distance, spray booth temperature, spray booth
air velocity, rate of solvent evaporation, etc. If this is a major problem
that is causing you production delays, you might want us to work with your
contractor on a consulting basis to resolve the problem. We would visit his
site and standardize all of the parameters that affect the perceptible color.
You asked about my next class. Yes, it will be held in May, and we are currently
selecting a hotel and finalizing a contract. We should have the details up on
the web site within the next week.
Please call me if you would like to discuss this further.
Best wishes,
Ron Joseph
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