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Letter 31035
Problem getting consistant purple dye
after clear chromate
++++
I AM EXPERIENCING A TECH DIFFICULTY WITH USING A PURPLE DYE ON
NUTS THAT ARE ZINC PLATED WITH A CLEAR CROMATE. WE ARE PLATING THE
PARTS THEN DIPPING IN CLEAR AND THEN DIPPING IN DYE. WE ARE HAVING
TROUBLE KEEPING THE DYE A CONSISTENT COLOR AND ARE GETTING A VARIETY
OF COLORS. WE HAVE CHECKED THE PH IN THE DYE AND IT RANGES FROM 3.5
TO 4.5. WE ADDED WHITE VINAGEAR TO DILUTE THE PH LEVEL AND HAVE FOUND
SOME SUCCESS. WE ARE UNDER THE GUN AND NEED A SOLUTION FAST. CUSTOMER
IS KNOCKING ON OUR DOOR. IS THERE A SPECIFIC FORMULA WHEN MIXING THE
DYE OR SOMETHING ELSE THAT SHOULD BE ADDED. PLEASE HELP
Joseph J Kolacsky
PLATING - CANTON, OHIO, USA
++++
Acid zinc deposits iron in random locations as a function of
current density, then where the iron is rich the dye color will vary.
Also the wetters in acid zinc are tenacious and interfere with the
uniform conversion of the clear chromate, so insert a 1/4 %/vol HCl
dip between the zinc and the chromate. Any dye will have a different
shade at 3.5 pH then is has at 4.5 pH.
Vinegar contains organics other than acetic acid and these
impurities interfere with the uniform adsorption of dye. Go get some
reagent grade glacial acetic acid.
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