Cr3 yellow

From my days working in the plating company 40 years ago, we could stop at nickle plating which gave a slight yellow, versus continuing to the next step shiny chrome.

Some old car parts were nickle plated into the early 30's for sure. Chrome stands out like a sore thumb against nickle plated parts.

Speak with "Metal Colours Ltd." -they are experts in the Cr3 processes.

The reason Cr6+ is forbidden is that it is a known cancer causing agent. If you are electroplating from a Cr6+ bath (2 step process), the chrome will plate as Cr6+ and reduce to Cr3+ directly. As far as I know the only issue is when the Chrome is in the bath, not once it is electroplated . Or are you not referring to electroplating?

SEE:

http://www.dynamix-inc.com/ProductList.html#chromates

Dynapass Tri Yellow Additive.

The yellow trivalent chromate finish does not offer any addional value as did the yellow hexavalent chromates. Yellow hexavalent chromates were specified when additional corrosion protection was required. With the trivalent chromates the yellow finishes and the "silver color" finishes offer the same corrosion protection as the yellow trivalent finish, but there is the additional cost of the yellow dye. Still for identification or color matching or even from habit, the yellow trivalent finish is specified.

I believe that the "chromating" process he is referring to, is not chrome plating. It is usually from a immersion dipping process in chromic acid, after either, plating of zinc or cadmium. Or it can be applied directly to aluminum (after cleaning and surface preperation). The chromic acid is a made from chromium. Their are two types of chromic acid. One is tri-valent, the other is hexa-valent.

Chromating offers a small amount of additional corosion protection. The sliver color is really a clear chromating. Zinc, cadmium and aluminum are all white (silver cloured) metals. Clear chromating offers a lesser degree of additional corrosion protection, than yellow. The longer in a chromating bath the more corrosion protection is applied, but to a limit. Olive Drab coloured chromating offers the best corrosion protection.

Hi HaroldSJC,

Yes, it is chromating, or may be called passivation after zinc plating process. It is not chrome plating.

Now we only use Cr 3+, and the color is "silver".

The question is what is the next step to make the surface become " yellow" as we did with Cr6+, only for aesthetic

Thanks.

Chromating comes can be made in different colours. The three most wideley used colours are: clear, yellow and olive drab. IBM specifies a red and a blue for identification purposes of fasteners.

As far as yellow chromating goes; if you are doing it yourselves, then consult with any chemical supplier who sells plating processes. They will be more than happy to sell you the necessary chemistry to make up a yellow chromate bath.

You used the word, "aesthetic" in your previous statement. In most peoples opinion, their is nothing "aesthetic" about yellow chromate. If you are refering to the prismatic irridencent effect that a yellow chromate leaves, well I guess it's in the eye of the beholder.

You never stated what the base metal is! Is this a plated item? Or do you desire this finish for an aluminum item? When aluminum is chromated, it appears to look like it has already has a layer of corrsion on it. But that is the purpose of chromating. When any metal has a corrosion protective or inhibiting finish on it, (except nickel and/or chrome) it is a controled oxide of the plated finish or of the base metal, as in the case of aluminum. The aluminum chromating is not to be confused with anodizing. Anodizing can be done in most any colour that you desire if, your item is aluminum. Depending on who does it, the colour can be uniform as it is applied to every part that you are processing. Anodizing is a true and controled thickness of aluminum oxide. Chromating is usually not measureable by a micrometer or any thickness measuring device, like an XRF.

I hope that helps you.

Our supplier do chromating for the screw, hinges and so on.

It is steel base, then zinc plated and finally chromating.

Before we did with cr6+ chromating, the color is "yellow"

Now cr6+ is not alllowed any more, we use Cr3+ and the color we get is "silver".

We want a "yellow" finish and we would like to know any kind of Cr3+ solution that give the yellow finish. How about the cost?

Sorry for the poor grammar! Been up for a while. But I think you get the message despite my out-of-character mistakes!