Dear Mike, >Ferric chloride is tricky, but preferrable to messing around with >acid. I find that getting a good quality etch resist is of >paramount importance. The photographic process is tricky, but >with a lot of trial and error good results can be obtained. Like >anything, the more you do, the better it will be.
Your reluctance to use acid mordants is understandable, but they can make a big difference with some materials. For red brasses, strong nitric acid, with about 10% added HCl to keep the tin oxide in solution, works for deep etching. Many brasses may give better results if potassium chlorate is added to the ferric chloride. For stainless steel, ferric chloride, hydrochloric acid, and water, about 5:1:6, will do. Aluminum does well with about 9% copper chloride in 1% acetic acid. I have used sodium hydroxide, "household lye," on aluminum. For the acid etchants, after rinsing with lots of cold tap water, baking soda solution will neutralize residual acid. Likewise, in the case of aluminum etched with base, a post water-rinse wash with dilure white vinegar is a good idea. All of the mordants require care against skin contact and fumes. They are best used either out of doors, or in a room with forced ventilation. (Open windows and a fan.) Unless you have access to a fume hood, they are not good for wintertime activities. Like you, I have used (solid) asphalt roofing "tar" for masking. Adding some paraffin wax seems to improve its working properties, at least in my hands. Candle stumps often have a melting-point that is higher than that of wax sold for food-canning use. These etching techniques are interesting and photo-resist use is important for mass production, but for the amateur making one-of- a-kind dials, engraving has much to offer. It is "classic" to the dialing art, it is direct, and it doesn't take much equipment. I use burins made from concrete nails. The large ones of the cut- nail type have a handle tang ready made. They can be annealed in a pottery kiln, a charcoal-fired hibachi, or with a propane torch. After a little forging and filing to give a diamond section tip, they can be reheated cherry red and plunged into tepid water to harden them. Drawing is done with the cutting end held in pliers as the tang end is heated in a flame. Water stops the process. The handle is best shaped like a mushroom, with the underside cut away to allow a low angle approach to the work surface. The end is ground flat, and the tool is pushed to incise the metal. A two hand grip with the whole-hand muscles working in opposition seems best for control. You can also make tools using lathe tool bit stock, mounted transversely in the end of steel round stock with a set screw, like a boring bar, but set to cut endwise. For straight lines, a knife-like ruling graver can be made with a piece of broken-off hacksaw blade "sandwiched" crosswise in a hardwood handle. The cutting tip is ground to a vee and the face squared off to meet the work at nearly a right angle. This tool is pulled along a straight edge. You can practice using these tools on aluminum flashing stock or the like before tackling valuable brass. A layout setup can be made on a sheet of plywood or heavy chip- board, like an oversize protractor. The graduations can be laid out by successive divisions with trammels or dividers. They can be extended to raised linear strips glued and nailed at the edges of the rectangular base board. (A hand calculator with tangent functions used with a linear scale laid on the raised edge-strips of the rectangle can also be used to mark accurate graduations.) Bigger really is better here, as any errors tend to be minified at the smaller radius of the dial. (You can get a larger layout on a given size board by marking a quadrant and repositioning the work by 90 degrees between marking the halves of the dial.) A vertical steel pin is mounted at the center point. A strip of plywood, with a straight edge attached, has a vee notch on its end which is held against the pin by hand pressure. The notch is aligned on a continuation of the ruling line so that drawn radial lines originate at the point the divisions are centered on. A snug hole drilled through the work accepts the pin when the work is mounted in place on the rig. The work can be mounted on a wooden support with hard roofing tar (an electric oven is great for doing this) and should be shimmed up to the height of the graduated edge strips. A coat of shellac-based white undercoat, of the sort used to "kill" knots before painting wood, gives a surface that will take pencilled guide lines and notations. It can later be removed with alcohol as solvent. The actual dial layout is done directly on the metal, without risk of errors as incurred at transfer by intermediate paper patterns, etc.. >By the way does anybody knows how to get color into the >negatively etched lines (or for that matter engraved lines). You can black-oxidize brass with a solution of about 75% nitric acid in which copper wire has been dissolved (with heat) until no more is taken up by the acid. (Leave some copper pieces in the storage container.) The brass must be pre-heated and ideally be dipped into the solution, but an applicator swab can be made of cotten sheeting wrapped and tied to a stick. The metal is wetted and then reheated with an air-rich oxidizing flame played upon it. Repeat the process 4 or 5 times. The metal will first turn green, then black. Cool and wash under tap water and finish with a baking soda rinse. You'll still have to rub or buff the bright parts clean with fine abrasives. The whole process is messy and a lot of work. I have had good luck with rubbing on a mixture of lampblack and boiled linseed oil. The excess is wiped from the surface with a tightly bunched smooth cloth pad slightly dampened with solvent. Leave the surface exposed to full warm sun (again, a summertime project. The heat and the U.V. light helps polymerize the oil. You can also bake the dial in an electric oven at low heat.) Later you'll want to repolish the surface and remove any residual coating which might weather unevenly. Still, it is pretty easy to do. I don't know how long it will last, but it is pretty durable, and could easily be renewed. >Finally does anybody think we should form a newsgroup? My own vote would be against it. I think all aspects of dialling are appropriate for the list. This thread's spate will wane after a bit, but I for one, would like to find further such entries about it here, sources of information and materials, etc., along with dial history, discussions of esthetics, literary references, and so on, whatever diallers care to offer. Bill Maddux. End.
