You have probably seen the yellow iridescent screws that were often found on cars? These were first galvanised (silver layer) and then received the well-known yellow chromate layer. However, these coatings are banned nowadays because the production of such coatings required chromium-VI, which, however, also pollutes nature in the course of time and also has very toxic effects for humans because the chromium-VI also dissolves from the coating.
In the course of time, there has been a lot of research into creating a chromium-VI-free yellow iridescent coating. In the meantime, it is possible to produce a yellowish layer from solutions based on chromium III, but these are not as thick as the original ones made of chromium VI. These are also visually yellowish, but not the yellow and not as iridescent as originally. The corrosion protection does not yet reach the old values, but it is quite close.
Unfortunately it is not that easy
It also has to be said honestly: you can hardly get high-quality yellow galvanising (yellow chromating) in a hobby cellar. But we are also working on a solution to produce a high-quality yellow chromating, but we have not yet been able to achieve a high-quality result.
What is the alternative?
Due to this development, the automotive industry nowadays uses zinc-nickel coatings, which achieve a very good protection due to the protective combination. In particular, zinc-nickel is used here in the area of parts at high risk of corrosion.
If you want to know more about zinc-nickel, you can read about it here: Zinc-nickel