AKA two sided spray etching AKA chemical milling
Our system is a Rotaspray Photo Etching System
A series of photos from this process can be found here

This process can be utilized to make highly accurate small scale sheet metal parts with both detailed etching and piercing and exterior cuts. It is commonly used on:
  • Any copper based alloy
  • Silver based alloys, as well as fine silver
  • Iron based alloys
It can also be used, but is not commonly used, on gold, aluminum, and other metals

We commonly etch thin brass, nickel 'silver,' and sterling silver.
We use Imagon photopolymeric stencil material
For higher degrees of accuracy, or for volume/greater material variety and speed we commonly send our parts our to Aculine etch of Seattle, WA. They charge a flat fee per plate etched (usually stainless steel), plus a single film charge per job. They like to lay jobs out themselves; you can see how they want you to layout your art here (mainly for business cards)

A workflow...this is not designed to substitute for an in person demonstration with notetaking.

This process starts with artwork preparation. The best candidates for this process are highly graphic designs where both external cuts, internal cuts, graphic etching, and a need for multiples are combined. When all of these variables are maximized, this is likely the most efficient process possible for producing metal parts. is an old design of mine for an earring card.

After I "pasted" up my art in an Adobe Illustrator file, I printed it off onto acetate with our LASER printer, and then prepared a 6x12" sheet of brass by covering it with ImagOn.

The sample files, for reference only, used in the demonstration are and

Placing the artwork over the photostencil, I exposed the artwork to UV light to cure any of the ImagOn that was not beneath black art.

Once it is exposed, the uncured stencil is washed out in 'developer ' until metal is exposed. This process is repeated on the reverse, with the pierce sections of the design mirrored and aligned, and the etch sections missing or altered to reflect the front/back.

Then the plate is exposed to heated ferric chloride in a spray bath.

Eventually, the acid will eat precisely half way through the material, allowing the 2 sides to meet and the parts to begin to fall out of the plate. The photomask is then eaten off with concentrated developer, and the part is done.