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Yellow chromate, whats the secret?

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  • Yellow chromate, whats the secret?

    I have read about 20-30 posts on here with folks having problems with the yellow chromate. Add me to the list...

    Chromating for 3 seconds or so (what the manual states), does nothing. Chromating for 40 seconds or so, gives a nice color. (PS. I didn't recieve chromate crystals, but a chromate solution)

    As other users have mentioned, touching the chromate while its wet, wipes it right off. When its dry, its much more durable, but a forceful application of my thumbnail wipes it right off. Is it supposed to wipe off when wet?

    I have read tons of posts on here about this, and still have questions:

    1) How durable is the chromate supposed to be

    2) Does the chromate "harden" with time? Will it be more durable after a week or two?

    3) What are the most common reasons for the chromate NOT working? I have seen posts where it was recommended that the acid dip be skipped. Other where it was recommended that one dip for a longer period of time. Some folks recommened more time flushing the newly plated pieces with distilled water. Others have recommended tap water.


    More washing time?

    More/less time in the acid dip?

    More drying time?

    Has anyone achieved a VERY durable chromate finish? Whats your secret? The parts look great...but I really don't want to be redoing all of them any time soon...

    Any help appreciated. (PS. I am following the new manual to the letter, when it comes to plating/chromating).

  • #2
    Re: Yellow chromate, whats the secret?

    yes chromate will come off unless it is left for time. It does become more durable, as in it should only come off with abrasive methods. I hang my bits for 24 to48 hours, depending on season, before handling, I then relief all my bits anyway at 200 deg C for 2 hours. If it is coming off after say 24 hours air dry, the underlying zinc was not active. Here is my process.

    directly after after zinc plating go to activating. this step is really to give a nice bright surface.

    if the parts have been left for any length of time post plating, then degrease and rinse before activating.

    Activate in a 10% sulfuric acid dip for about 30 seconds.

    HOT WATER RINSE (hot tap water) for a few seconds and then use a spray bottle with distilled water to thouroughly rinse. Do not handle the parts at all

    chromate for 30 seconds and lift the item out of the solution slowly or the coating may damage.

    imediate HOT water dip gently. SLOWLY imerse and SLOWLY move around without touching the sides of the container for 15 to 30 seconds.

    slowly lift out and hang to dry. I use a hot air gun and halogen lights to get the parts to dry quickly. you can use compressed air, but less than 15psi to help remove water and only at a distance.

    so far I have only had one part peel and that was because it is my bitsa test piece. It has been plated about 10 times with various coatings.. copper, zinc, nickel.

    Hope this helps


    • #3
      Re: Yellow chromate, whats the secret?

      Originally posted by bpu699
      BRIGHTENER! DO NOT USE IT w/parts to be yellow chromated.

      I have found that yellow chromate is not as durable on bright plated parts. Others here say otherwise, but I get far better durability on parts plated w/out the "brightener".

      Chromating for 3 seconds or so (what the manual states)
      I don't know which manual you have, but mine states 30 - 60 seconds. 3 seconds will do virtually nothing (it's probably a typo).

      Immersion time will depend on the finish you're after. Shorter times result in lighter yellow w/more iridescence, longer times result in darker yellow w/less iridescence. The strength of mix also results in different depths of color & iridescence. You just have to experiment to see what gives the results you're looking for.

      Is it supposed to wipe off when wet?
      Yes. Fresh chromate is quite soft and will rub right off. It has to be given time to cure.

      I have also found yellow chromate to be UV sensitive for up to 48 hours after chromating. I leave yellow chromated parts to cure for 4 days in shade before handling.

      How durable is the chromate supposed to be
      When done properly, it is very durable.

      As for acid bright dips, it is not really necessary if you chromate immediately after plating, but does help a bit. All chromates are acid based to begin with, so are in effect "self brightening". A pre-chromate bright dip does still improve the look, but only slightly.

      Yellow & clear chromates are nitric acid based, black chromate is sulphuric based. Use only nitric or muriatic bright dips for yellow/clear, and only sulphuric for black.

      You only need to dip the parts until it stops brightening. You will be able to see it changing color, when it stops changing, that's enough. How long it takes depends on the type & concentration of acid.

      DO NOT LET the parts dry at any time between plating & chromating! Do it quickly & keep them wet at all times. As KCV6 said, if it's allowed to dry before chromate, then you must reactivate in an acid dip.

      Seans Zinc Plating page


      • #4
        Re: Yellow chromate, whats the secret?

        Thanks guys...

        I didn't know that you can't handle the parts for a couple of days!!! I thought that the part was good to go after the chromate dried.

        I am using the brightener. I have read conflicting reports on its use. The chromated parts look much better after the brightener, and much more "original." Without the brightener, they just don't look right, and have a matte finish.

        The parts I am replating were originally very shiney/gold cad...


        • #5
          Re: Yellow chromate, whats the secret?


          First of all, thanks for all of the information that people are posting here. It is both interesting and helpful.

          So, has anyone come up with a definitive method for the yellow chromate slough-off problems? I purchased one of the cad/zinc kits + trivalent yellow chromate. I am getting EXCELLENT results with everything but the chromate durability. I have tried many of the suggestions & methods that I have read in this forum. So far, KCV6's method has shown the best results. Let me caveat that by saying that I used muratic acid instead of sulferic acid and it only works without the zinc brightener additive -- as seanc has stated several times. With brightener in the electrolyte solution, the chromate comes off in the post-chromate water rinse. With KCV6's method, and the absence of brightener, I get OK results, but the chromate will have good adhesion properties in most places, while rubbing off in others.

          As far as my setup (temps etc.) it is mostly all by the book. I use a CC power supply and I calculate the surface area of each substrate item down to 0.001 inch accuracy -- even taking into account the surface area of the wire conductor. My only change to the book is that I clean each item in an ultrasonic cleaner BEFORE I begin any of the Caswell process. My plating results are outstanding.

          I am hoping through others experiences and knowledge, that can get a good method down for the chromate.


          • #6
            Re: Yellow chromate, whats the secret?

            OK, I’ve been doing quite a bit of experimentation and analysis on my own to see what I could find to aid in the prevention of Yellow Chromate slough-off. Here is what I have found:

            The Trivalent Yellow Chromate does not have good inherent adhesion properties. Using extra careful preparation, removing brightener, and using drying techniques can yield decent results – but not great. For a while, I was able to achieve the best results by not using brightener and using KCV6's method. I was also able to achieve decent results eliminating the bright dip after plate. I believe Mr. Caswell himself suggested this method.

            In further experimentation, I ordered some Blue Chromate from Caswell and it has excellent adhesion properties. Adhesion is great even with the brightener. A little research and questioning led me to what I believe is an outstanding Yellow Chromate solution. The process is as follows:

            1 -- Clean, degrease, and plate per the Caswell book. Whether you use brightener or not will ONLY affect the brilliance of the finish – not the durability.
            2 -- Immediately after plating, spray bottle rinse the plated object with distilled water, followed by a bath rinse in distilled water, and yet another spray rinse. Rinsing if very important!
            3 -- Submerse and swirl the object in the Blue Chromate bath for 20 ~ 40 seconds.
            4 -- Remove object from the Blue Chromate and give it a quick spray bottle rinse with distilled water.
            5 -- Submerse and swirl the object in the Yellow Chromate bath for 30 ~ 30 seconds.
            6 -- Remove object from the Yellow Chromate bath and spray bottle rinse.
            7 -- Quickly remove excessive water using non-contact means. For fasteners and brackets, I have found that compressed air at about 20~30 PSI from about 10 inches away works great. If you don’t have an air compressor, they sell cans of the stuff at electronics stores. The object does not have to be completely dry, just no water drops.
            8 -- Finish drying with a heat gun or hair dryer. If you use a heat gun, don’t get it too hot. 150 degrees F. is ideal.

            At this point, you should not be able to rub off the Yellow Chromate very easily. I then hang them up overnight for a little extra cure time.

            Using this method, I immediately noticed several differences. First, the colors are much closer to “factory” Yellow Chromate colors. When I was using the Yellow-only on zinc + brightener items, the color looked more gold and was lacking the translucent reds and greens that I often associate with a Yellow Chromate finish. Now, with a blue pre-dip the colors are more evident. It looks factory fresh or usually better. Second, the durability of the finish is far superior to all the other methods that I tried. Normal tightening and loosening of a fastener (with a clean wrench) did not damage the chromate finish. Slipping a wrench, or gouging the object will damage the chromate finish but that is to be expected.
            Last edited by kxkraze; 10-17-2007, 12:39 AM.


            • #7
              Re: Yellow chromate, whats the secret?

              A quick update on my chromate research:

              I have been having good success with the blue and yellow chromate method that I posted earlier. One remaining problem that I would encounter from time-to-time was that if I had a post-chromate, post-rinse water bead (in a threaded hole of a bracket for example), when that water bead rolled down the bracket, it would sometimes leave wash marks on the yellow chromate.

              I called Caswell and found out the manufacturer of the blue and yellow chromate. I then called the manufacturer and talked to one of their techies for a while. They had the following information to offer:

              1) Use sulferic acid (1% in dist. water) as a pre-chromate dip, followed by a double rinse in dist. water. They recommeded this over nitric acid even. The purpose of this dip is to remove organic residues that might exist from the plating solution. Failure to perform a pre-chromate dip will eventually contaminate the chromate as organics build up. There are tools to test for chromate contamination but signs include a yellowish tint in the blue chromate and a lack of color in the yellow chromate.

              2) Following chromate, double rinse in dist. water. Dry in cool to luke-warm air first to remove excessive water. Use hot air (approx. 150 deg. F) after all water droplets are gone. The reason that he gave not to go straight to hot air is because if a water droplet is heated and then runs down the object, the hot water droplet can cause an unwanted blemish.

              3) Allow to air cure for 48 hours before any handling of any sort.

              4) For the ultimate in corrosion protection and durability, follow the 48 hour cure time with a hydrogen embrittlement removal by placing them in an oven (toaster oven, etc.) at 375 ~ 400 Deg. F. for 2~3 hours.

              Anyway, I just thought I would share the information that I received today. I have not tried any of this yet but I plan to this weekend. I will post back later with the results.

              BTW -- due to the posts on this forum regarding sulferic vs. nitric acid, I questioned him about this several times - up to the point where I sensed he was getting annoyed. He said that they not only sell the chemicals but also have a plating plant in which they use their chemicals for large contracts. Hey said they use a 1% sulferic dip exclusively for all of their pre-chromate dips. He said nitric will work but sulferic is better.


              • #8
                Re: Yellow chromate, whats the secret?


                My problem is when I use low air pressure from an air gun, the gold chromate comes off in chunks. It just blows off and the part is ruined.

                I have stopped using brightener, per the posts here. But the parts are duller, so I would like to use the brightner in all Copy Cad plating processes, zinc or gold chromate.

                Additionally, my anode is getting black after each part is plated. I plate for six minutes then turn the part around for full coverage, using two anodes on one side of the 4.5 gallon tank.


                1. Brightener or no brightener?? I would prefer to use the brightener!!

                2. Use low air pressure and chance the sloughing off of the gold chromate?? Or, what do you recommend?? Does the Blue Chromate help keep the gold chromate on the part??

                3. I tried using a heat gun, but the drips and drops kept coming, so I went to low air pressure and the gold sloughs off!!

                4. My kit is over four years old, and I was not sold a air source in my kit, should I buy one?? There seems to be black particles on larger parts, so perhaps the air system would help.

                5. Should I use bandages over my anodes to reduce blackening anodes?? Currently, I use a scotchbright pad after every six minute plating session per side. This is adding a lot of time to my plating jobs!! I do not remember the anodes turning black except after every 4 plating sessions, now it is after each one half session (remember I plate six minutes and turn the parts around.)

                6. I have the older Copy Cad system, so should I keep my solution at the lower end of 80 degrees to 90 degrees??

                Thanks in advance. Tom


                • #9
                  Re: Yellow chromate, whats the secret?

                  Hey Tom,

                  Definately give your tank a filter through some filter cloth, sounds like you have a good build up of smutt from the annodes in the bottom (little black bits).

                  Definately bandage the annodes. Get a cheap close weave polyester business shirt and make up some annode bags, by at least doubling up the material and stitching on a sewing machine into bags that will fit over the annodes. Secure in place with big rubber bands. The more layers the better.

                  I gold chromate on brightened parts, see my brake parts in my gallery, these were all extremely bright and shiney and within 2 days of chromating the chromate was hard as!

                  Get a aquarium air pump and make up a bubbler to agitate the solution (thats if I'm reading correctly and you don't already).

                  This should all help.


                  Mark Smith


                  • #10
                    Re: Yellow chromate, whats the secret?

                    Hi Mark,

                    I will try all of your suggestions.

                    Do you think this will stop the sloughing off of the gold chromate?

                    Thanks, Tom


                    • #11
                      Re: Yellow chromate, whats the secret?

                      Hey Tom,

                      The Gold Chromate is always fragile until cured, especially on bright shiney zinc surfaces. However if the zinc to be chromated is fresh from the plating tank and nice and warm, this helps.

                      I rinse my zinc bits from the tank in really hot tap water in a rinse bucket and then rinse off with distilled, then do a quick activate, rinse (distilled) and then straight to chromate. Even pulling the items from the chromate tank too fast can cause the chromate to pull off on and around edges. I then carefully rinse with a misting bottle over the chromate tank so as not to drag and waste chemicals. My next step is to slowly imerse in hot water for a few seconds, I then leave to air dry for a few minutes and if needed use a hot air gun to blow excess water off. This is less than 10psi, just a standard wagner paint stripping hot air gun.

                      Hope this helps


                      • #12
                        Re: Yellow chromate, whats the secret?


                        I don't know if you have found a solution to your problem yet or not but I will share with you what I have found and works quite well.

                        1) According to the caswell employee that I spoke to, this is the place where they buy the chromate in bulk. Now you have instructions directly from the chemical manufacturer.

                        2) The best method that I found for using brightener and not getting slough is to perform a blue chromate dip for about 40 seconds followed by a yellow chromate dip for a duration up to desired color. I then double dip rinse. First tap water then distilled water. Next, I hold a hair dryer about a foot away and blow any drips away with very light air pressure. You can even just use your breath. You can use a heat gun but be careful not to exceed 150 degrees. The EPI rep. warned me that it can have negative effects. When there are no more water dropletts visible, I place the object in a toaster oven at 150 deg. F. for about an hour. This rapidly speeds up the curing process.

                        I don't know exactly why the blue chromate was my problem solver. My best guess is that the blue chromate has better "adhesion" characteristics when interacting with brightened zinc. It then acts as a foundation for the yellow chromate. Regardless, it works.

                        Regarding the darkened anodes -- mine are almost always dark and they have no ill effect on my plate.


                        • #13
                          Re: Yellow chromate, whats the secret?

                          Thanks Mark and Kxkraze, looks like I have a lot of work to do bringing my system up to both your current specs. I'll let you know how I make out.



                          • #14
                            Re: Yellow chromate, whats the secret?

                            This is interesting. I've never had a problem with chormating any of my parts and I've been doing it for over 3 years (prior to Caswell's release of the blue stuff). Rinsing between plating and chormating is a very important step (as others have pointed out). My parts usually take about a 30min dip. The amount and look of the iridescence will not be apperent until the part has dried. For me personally I have a rack that I put the newly chromated part on and when I come back to look at them after 15 min or so in front of a small space heater they look absolutely stunning.

                            I would like to know the deal on the brightner msyelf. I never ran into any problems with it but I liked that really shinny look that I was constantly adding it and kept running out. Does it make sense to maybe polish the part first and then zinc plate without brightner?



                            • #15
                              Re: Yellow chromate, whats the secret?

                              I just ordered Blue Chromate from Caswell today. Cleaned and filtered my solution. Interestingly, a old anode was at the bottom of the solution and it was about 2 inches by 2 inches. When I ran five strings of parts today, the anodes were still graying after that. I also ordered anode bandages from Caswell too.

                              I tried the 150 degrees F for an hour and using the paint stipper heat gun to get the water drops off the parts after Gold Chromate dipping.

                              Parts were better than before, but some sloughing, but not much!! Yippee!!

                              Here are my questions.

                              1. The Caswell Gold Chromate runs at 80 degrees F, do I need to heat the Blue Chromate too?

                              2. Agitation. How do you keep the air system at the bottom of the tank to generate aeration? Do you expoxy the air line to the bottom of the tank? I have a four gallon cylindrical bucket.

                              Thanks in advance, Tom