My design for the back plate was to etch the design of Durin’s Door all the way through a copper plate to allow light to shine through. I used acrylic as the backing to hold the free-floating copper pieces in place. Of the options of clear adhesive that bonds to both plastic and metal I choose goop.

Step 1. In designing the back plate I stared with the phone. I wanted it to sit in a 3”x6” void to allow for the phone to slide down and seat with the plug. So that void was X by Y+1”. I needed the copper to inset into a 0.5” channel so I needed the copper sheet to be 4” (X+1”) wide. The copper sheet needed to go above the phone void and into the channel, so the sheet had to be 7.5” (Y+2.5”) tall. I angled to a narrow top to inset the iWatch charger. I used tin snips to cut the copper sheet to the desired shape.

Step 2. Create the mask. I used the laser printer toner transfer method to make my mask. The most complete explanation of the process I have found is here: http://fullnet.com/~tomg/gooteepc.htm . I wanted my phone to block the light while charging, so I needed the image to be smaller than 3”x5”. The acid will eat through whatever is not covered in the black toner, so I had to find a color inverted image, and them mirror image the print.

Step 3. I used my iron to transfer the toner from the page to the copper sheet. For a good transfer the copper sheet needs to be completely smooth and clean. Any defects will affect the toner transfer. At this point I have found that black nail polish is a quick and effective way to cover up holes in the mask.

Step 4. I used the goop to attach the cooper plate to a layer of acrylic. On this step there are several things to remember. First, be sure to get good coverage with the goop on the back of the copper. The glue will act as the resist on the back side of the copper once the acid has eaten through. Second, your acrylic needs to be smaller than the copper plate but fully cover our image. I used an acrylic knife to score the acrylic at the desired breaks, then applied force to the acrylic to snap it at the scored edges The space will allow the led to sit next to the acrylic in the pocket. Finally, I did a test etch with my material to see if the acid would dissolve the goop. In my short duration test it appeared fine, but in the final product I noticed the goop was dissolving and interfering with the etch. If you have options, I would recommend testing other adhesives’ resistance to acid. If you find a good one, please post it in the comments.

Step 5. I used duct tape to cover all the large portions of exposed copper. After everything was covered up that I didn’t want etched I dropped the copper into the acid. I have found that if you turn what you’re etching upside down in the acid, but set it on “feet” that raise it off the bottom of the basin, it will etch faster. The only issue I had was that the goop slowly dissolved in the etched portions and flowed through the holes made by the acid, so in this situation the slower etching while right side up would have been preferable. Be sure to check the etch periodically throughout this process. Mine ended up etching for about 4 hours. During that time I used the nail polish to patch a few holes in the mask that appeared when some toner flaked off. Just take the piece out of the acid, and use water to dilute any acid still on the metal to stop the etching process. If you just want a copper back plate with no light shining through you can use a similar process to what I used for my cuff build: https://www.instructables.com/id/Tengwar-Elvish-Copper-Cuff-with-a-Patina/step2/Crafting-the-Parts/ .

Step 6. Once you have removed the copper, you have to remove the mask. I generally just hit it with sandpaper until all the copper is exposed. Once the copper is exposed, you apply your patina solution. This solution accelerates the oxidation process. Different solutions will provide different colors. My solution produces a blue and green patina. The salt content is the primary method to control the green content, and ammonia controls the blue. You can just wipe the solution onto the copper, but I like to spray it on with an old cleaning solution bottle (adds to the randomness). To get a good patina will take a couple days. Reapply the solution every 12 hours or so. After you are done growing your patina, spray it with a sealant like polyurethane to preserve it in the desired state.

Step 7. To build the frame, I used a router to inset the 0.5” channel in the dowel. I them measured out my cuts and used a table saw that can be adjusted to make angled cuts. If you are using a hand saw, I would recommend investing in a miter box to cut precise angles. I used the router again to excavate a pit to inset the iWatch charger. I added a bit of scrap wood to the top to look like a key stone. I used a saw to make some quick rough cuts in the base to allow the cords to run through. You should apply a quick stain, especially if you are using different types of wood. Then glue all the pieces together except the base.

Step 8. I used sand paper to rough up the acrylic. Roughing the acrylic will help the light to refract out the etched holes. Then I glued the second sheet of acrylic to the back of the first. On the second piece of acrylic I sprayed the back with some silver metallic paint I had. I hope that will increase the light shining through. Slide the whole back plate with lights into the frame. Finally, glue the base onto the frame with the led cord running out its hole.