There are many ways to blacken both electrodeposited and cast zinc and its alloys. We have solution formulations in our technical library dating back to 1896 literature (Metal Colouring). Over the forty five year history of Anoplate, most blackening systems have been used at one time or another.  The various older baths used molybdates, sulfides, dyes over
chromate films and other chemistries. Many seemed prone to degradation by water or other corrosive environments. The black dyed
olive drab chromate had great corrosion resistance but was difficult to run consistently, making it a troublesome production process. In recent
years newer post dip chromates have been offered, with good black characteristics and acceptable salt spray performance. It is important to
note that with equal thickness, the black chromated zinc alloy deposits versus black chromated zinc, protects steel for a longer time. This is
possible since the zinc solution modifier (iron, nickel or cobalt), changes the corrosion potential by making the alloy deposit more noble. With respect to the protection of steel, zinc-iron deposits give anodic protection, just like pure electroplated zinc. For more information ask us for reprints of our Fall and Winter 1998 issues of Anoplate News.

Most of the zinc blackening processes in use today are olive drab (OD) chromate based, containing silver. When first produced, the color is great, easy to use and has good corrosion resistance. Various factors, including light, may cause the black to go "maroonish" or less black at a early date. This does not always happen but with Murphy's Law it will on a critically cosmetic part. This is a industry wide concern. We recommend age testing before being used as a decorative finish. ANOPLATE CAN NOT BE HELD RESPONSIBLE FOR AN INDUSTRY WIDE PROBLEM
USING STATE OF THE ART TECHNOLOGY. 

Where do we go from here? Our newly installed zinc-iron alloy bath just might be the answer. With a zinc content of from 99.3 to 99.7%, it is for all practical purposes (not specification though) zinc plating. When it comes to corrosion resistance, results show up to five times (we like to use three times) the salt spray resistance. There is more good news however! The chromate used in this process does not contain silver and as a result is much more color fast.  This deposit does have limitations where high temperatures are involved. Zinc-iron deposits can also be chromated with yellow or olive drab films. Clear coatings are not recommended.

All of the above chromates can be applied to either galvanized objects or zinc die castings as well. The surface pattern as a result of casting or hot dip galvanizing will appear in the final chromate film. If this pattern is objectionable, parts can be easily plated with pure zinc, eliminating
this blemish. A complete cleaning line for plating over zinc die castings is contained in our illustrated 42 tank line. From huge plates and cabinets down to small finger sized objects, this hoist line is sized for your work. Let us quote your next package.