G’day Chris here, and welcome back to Clickspring. In this video I complete what will be one of the most viewed parts of the clock, The chapter ring. Traditionally this part might have been sent out from the workshop to be professionally engraved, but it was also common practice
to produce dials using chemical etching, and that’s the process I’m going to use today. This square of brass sheet will become the dial, and I’m going to use these other bits
and pieces to help prepare for the job. So let’s get started. I’ll be using photoresist film to mark out the design, and it needs a completely clean
alkili free surface to do its thing. So I scrubbed the surface with emery paper and household vinegar and then cleaned it off with acetone. The result was a clean fresh metal surface. I’m going to need this later on, so I’m mixing up the developer solution now. It’s a mild alkiline solution thats used to dissolve the unexposed photoresist. The photoresist reacts to UV light, so all work from here on must be done under a yellow light. And this is the photoresist. It’s a thin light sensitive film, slightly
sticky to the touch. It has 3 layers: The photosensitive layer is sandwiched between 2 removable coatings. It comes off the roll with a natural curve, and at this stage I’d like to uncover the surface on the inside of the curve. A piece of tape on one corner lifts up the protective coating so that it can be peeled off. It was then gently pressed onto the bare metal surface, and all of the air bubbles were removed. A gentle heat will bond the photosensitive material to the metal. I used a domestic iron set to low, over a sheet of paper, along with a little bit of pressure, and it worked great. Now if all of the preparation has gone well, then the bond will be strong, and the resist will be well attached across the entire surface of the metal. I’ve made a simple light box to expose the resist, and a sheet of glass sits on top to
position the work. The dial artwork has been printed onto a clear film. It was placed onto the glass surface with the emulsion side facing up, and then the workpiece was placed on top with the resist facing down. Of course everything needs to be quite still during the exposure, so I’ve got a few weights to place on top keep everything in close contact. And for my setup, three and a half minutes of light gives the correct exposure. The second protective layer was then peeled off, and the mild alkaline solution I prepared earlier, was used to dissolve the unexposed
resist. For the most part, the exposed resist forms a nice crisp line, but inevitably there are small printing flaws that need to be removed like these small dots. I scraped these off with the sharp point of the scriber. I also gave the artwork a touch up with some paint. When I made the graphic I had intended to have terminating rings on the inside and outside, but I’ve since come up with a different
idea that I’ll show you in the next video. so I painted over those rings so that they wouldn’t etch. I glued some small plastic risers on the corners to keep the plate above the bottom surface of the etchant bath, and I’ve also used clear tape to seal off all of the other surfaces. This center punch mark will help me position the work on the lathe, later on. So after all of that preparation, it’s finally time to do some etching, and the etchant that I’m using is ferric chloride. The chemical reaction is certainly faster and more effective if the solution is heated. I preheat it by sitting it in hot water, and then ideally an aquarium heater would be used to keep it warm during the etch. But I’ve found that simply putting the solution in direct sunlight has a similar effect. After sitting in the etch solution for about an hour and a half, the surface is nicely etched, and its ready for the next step. A strong alkaline solution is normally specified to remove the resist, but have a look at what a great job acetone does, its hard to beat that. OK so that’s the etching process complete. The etched surface is quite pitted, but the edges are crisp, and the overall depth is perfect for accepting the shellac wax.
What I need to do now is trim off this excess brass, and form the ring shape . Another job
for a super glue arbor on the lathe. Traditional dial wax is basically a colored shellac, so in its natural state its quite hard and brittle. But it melts to a sort of maple syrup consistency under a gentle heat. While its in that fluid state, it can be worked into all of the lines and numerals. And when it cools down again, it goes back to being brittle and hard, so the excess can be removed with emery paper. And that brings me to the final step that really makes the chapter ring come to life: The silvering. The silvering compound was mixed with a small amount of water, to form a thin paste, and then it was applied by hand. And then it was followed in a similar way with the finishing compound. A gentle heat with the torch finishes off the process, by melting the sanded wax surface,
and making it shiny again. A single coat of lacquer, and it’s done. In the next video, I’m going to take this chapter ring design one step further. Thanks for watching, I’ll see you later. If you’ve just found you’re way into this clockmaking series, thanks for checking it out. This is just one episode of a longer series where I show all of the steps to making a clock from raw stock, so be sure to check out those other videos. I also post other project video’s on making some of the tools I need to build the clock, And you can also find some more toolmaking info on the clickspring projects website. Thanks again for watching, I’ll catch you on the next video.