The Science

The Spray “Chroming” process has 3 stages. First the work piece is basecoated using a special resin paint to give it a very high gloss surface on which to “Chrome”. The next stage is the actual “Chroming” when the painted work is spray metallised using a waterbased chemical system which plates the surface with a very thin layer of pure silver metal. Finally a specially developed clear lacquer coat is applied to the metal layer using normal spray painting methods protecting it from damage.

Though the basic chemical process has been used commercially by the decorative mirror industry over many years as applied by the system purchased by our client was found to be completely unreliable. Apart from complete failure to metallise at all! there were an number of other failure modes apparent during our investigation, what we came to term “blush”, a cloudy white deposit over the silver which was particularly visible in strong directional lighting, reducer burn showing up as intense white or yellow-brown “burns” on the metal layer's surface. Other defects were yellowish silvering, mottled silver where the lustre of the silver varied in patches across the surface. A fault which we started to call “wetting” marks which was a pattern of spotty darkening of the silver's lustre resembling the pattern of wetting that occurred at the beginning of the silvering process.

Further investigation of the 3 main stages of the process found that there were, unfortunately serious shortcomings in all of them and it was reluctantly decided that there was no option other than to redesigning the process from scratch. Though a radical step this was seen by the client as a positive step since it would enable him to manufacture and sell his own range of chemicals and lacquers rather than the expensive and troublesome process of importing them from the USA It was necessary therefore to formulate or source base and top coat lacquers, a full range of silvering chemicals and to design a spray silvering machine.

Though having a wide range of skills Gammascience does not possess the special skills required for paint and lacquer formulation but were able to find in the aerospace coatings manufacturer Indestructible Paints Ltd and enthusiastic and skilful partner producing lacquers of quite exceptional clarity. Gamma Science also worked with Indestructible Paints to develop number of Silane based bonding additives to enable the lacquers to achieve a high bond strength to the notoriously difficult to bond metallic silver layer.

Having found safe hands to carry out the lacquer formulation, Gamma Science was able to concentrate on the actual silvering (“chroming”) stage. The process of spray silvering is achieved by spraying the surface of the workpiece sequentially with a number of different chemical solutions finishing with a dilute solution of a silver salt and a solution of a reducing agent being sprayed on to the surface simultaneously from a twin nozzle spray gun. Gammascience Ltd carried out extensive literature and chemical research culminating in the development of a completely reformulated system of chemicals for the process including adding an unique and pivotal stage to the process. In the process of developing the chemical system for the Astrachrome system Gamma Science identified all the important process parameter necessary for consistent metallization and was thus able to write the specification for the necessary equipment to carry out the process reliably. Used in the specially designed spray unit (also designed by Gamma Science see “Hardware”) the reformulated reformulated system of chemicals and lacquers took Spray Chrome Solutions' AstraChrome system from being the hit and miss system imported from the USA to a work every time system capable of industrial and commercial use.