George There are two issues here: the quality/thickness of the zinc plating and the chromate conversion. Assuming the former is OK, the latter appears to be your difficulty. The passivation forms essentially a layer of zinc oxide admixed with a zinc chromate. There are three zinc chromates and none of them are colourless. ZnCrO4 is yellow and is the result of most forms of chromatisation. If it is truly colourless, then the layer must be very thin, indeed. Remember that the light goes through the chromate, is reflected off the metal and back through the chromate again, so that, as a piece of coloured transparent plastic looks more intense in colour against a piece of white paper than when held up to the light, so it is with conversion coatings. The zinc oxide, itself, can enter into some acid reactions. One advantage of having coloured passivation, apart from thickness, is that you can see it's there! :-) I should imagine that the easiest rapid way of determining the quality of the coating may be by Auger analysis with comparisons against known samples. Brian Wenger, George M. wrote: > If a cold rolled commercial quality steel (per ASTM A366) assembly that is zinc plated (0.0002" min per ASTM B633 Type 3) and supposed to be colorless chromate conversion coated begins to show finger prints and surface tarnish in a relatively benign environment, should you suspect that the chromate conversion coating is missing or improperly applied? And secondly, is there an analytical method to determine the presence and quality of the coating or would one have to resort to Salt Fog testing > > Regards, > George > > George M. Wenger (908)-546-4531 > Reliability Engineer > RF Power Amplifier Group > Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 > [log in to unmask] > > > --------------------------------------------------------------------------------------------------- > This message is for the designated recipient only and may > contain privileged, proprietary, or otherwise private information. > If you have received it in error, please notify the sender > immediately and delete the original. Any unauthorized use of > this email is prohibited. > --------------------------------------------------------------------------------------------------- > > --------------------------------------------------- > Technet Mail List provided as a free service by IPC using LISTSERV 1.8e > To unsubscribe, send a message to [log in to unmask] with following text in > the BODY (NOT the subject field): SIGNOFF Technet > To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) > To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest > Search the archives of previous posts at: http://listserv.ipc.org/archives > Please visit IPC web site http://www.ipc.org/html/forum.htm for additional > information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 > ----------------------------------------------------- > > > > > --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------