Shop Note

A Simple Etching Process

Mike Taylor In the absence of a CAD programme on your computer, draw the items you want to photo etch about 4 times bigger than the size you want to finish up with, not forgetting the holding lines that will keep the item in place on the finishes etched sheet, then take the drawing down to your local photocopy sheet and ask them to reduce the drawing (by the factor with which you drew it) to the size you want and ask them to reproduce it on cellophane.

Armed with your negative, pop over to Radio Shack or any electronics store and get yourself a can of Photo Resist spray and also a can of Photo Etch Developer spray plus an ultra violet strip lamp. You will also need a plastic tank (old Tupperware box) a little larger than the brass or copper sheet you want to etch and enough ferric chloride to fill it to a depth of about a couple of inches.

The process. After cleaning the brass sheet meticulously to make it sine and to remove all scratches, wash it in clean water to get rid of the polish. Never handle the sheet again as this will contaminate it. Wear surgeons gloves.

In subdued light, (it doesn't have to be pitch black like darkroom conditions), spray the Photo Resist evenly over the brass sheet and leave to dry. Place the cel negative over the brass and place a clean sheet of glass on top to keep the cell flat on the brass. Wave the ultra violet lamp six or so inches over the glass for a few minutes, then remove the glass and the negative and spray the brass with the developer. The parts of the sheet that were not masked by the negative will chemically peel off and the sheet will have to be washed again to remove the exposed areas.

The next bit can be a bit dangerous so wear eye protectors and a respirator that will filter out harmful gasses, such as ferric chloride and keep the surgeon's gloves on.

Get a large wide saucepan and heat some water in the bottom of it. There should be enough so the ferric chloride tank floats in it. The acid has to be fairly hot to do its stuff quickly, as the faster one can etch then the crisper the lines stay. Insert the exposed brass sheet into the etchant and agitate the tank to keep the acid fresh over the etching surface. Check the process frequently making sure that the acid isn't burning too much away on the reverse side. To maintain the thickness of the brass during the etching process, coat the back of the sheet with a wide felt tipped pen or paint to mask it.

Once completely etched, wash the brass sheet in clean running water to arrest the acid action. Then clean the sheet carefully with fine steel wool. The sheet is now ready for use.
{Mike Taylor}

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