How to Plate Stainless Steel Black

Question:

How can I plate stainless steel to give it an antique black finish? One of my customers is asking for this process! 

Answer:

Stainless steel is blackened using a molten sodium/potassium dichromate bath. While the process sounds nasty, it is fairly widely used. The bath consists of 1 lb each of sodium and potassium dichromate. The bath is operated in the 750-800F range. All the usual precautions must be followed when dealing with concentrated, hot oxidizing materials. In addition you must deal with the environmental issues that go with hexavalent chromium.

I think your best bet is to contact some of the vendors listed in the “Suppliers” section of pfonline by clicking on Plating and Anodizing Processes, then Blackening Processes, Solutions or in the Products Finishing Directory and Technology Guide under Blackening Processes, Solutions. If you only have one customer who needs this finish you might consider out-sourcing the work. The American Electroplaters & Surface Finishers Society, 407-281-6441, publishes a Shop Directory each year that lists many finishing shops. One of the categories is black oxide finishes.

Question:

Our company has been asked to bid on a project that involves the blackening of stainless steel. The company does not call out any specifications. We have never performed this metal finishing process. What are some of the methods used for blackening of stainless steel? 

Answer:

I must say I’m a little bit surprised that your potential customer has not specified a process that should be used. That being said, listed in the chart below (Table I) are a few methods that have been used to blacken stainless steel.
Before you consider this project, it would be a good idea to discuss it in more detail with the company and find out exactly what properties they are looking for in the final finish.