Actually, I didn't set out to make a death ray. The items I found in my junk bins guided me in that direction. As with a lot of instructables, it's unlikely you'll have the same odds and ends I used to put this together. I just hope you can discover a new technique or find inspiration for a similar project.
Step 1: Assembling the Tanks
To add strength to the tank assembly, I needed to add a cross support in the middle. I used a short piece of 3/4" PVC for this. Using a hole saw with a diameter about the same size of the tanks, I drilled through a section of PVC to "fish mouth" both ends of the piece. After cleaning up the cuts with a hobby knife, I hot glued the the PVC between the tanks. Once the glue had set, I went back over the seams to leave a rounded bead of hot glue that would look like a weld after being painted. I used the fast setting type of JB Weld epoxy to assemble the copper fittings to the tanks. Next, I masked the face of the pressure gauge for painting and cut off the excess tape. I drilled a hole in the center of the copper T fitting and screwed in the pressure gauge. It screwed in snugly so I didn't have to use any epoxy. Finally, I used a corrugated plastic straw from a kid's water bottle and hot glued it into the top of the copper T fitting. This will conduct the liquid fire from the tanks to the death ray.
Step 2: The Ray Gun
To make it less like a light saber and more like a death ray, I figured I'd seat it in a piece of PVC cut lengthwise and attach something pointy to the end. The PVC was easily found. My wife suggested one of her cake decorating tips for the nozzle. I found one that fit perfectly.
I cut the PVC to length and then used a Dremel to cut it in half lengthwise. The PVC reflected the light from the light saber making it much brighter, as you'll see in later pictures.
I prepped the pieces, but I didn't glue them together yet. I wanted to paint them separately to make masking the translucent portion easier.
Step 3: Painting and Weathering
Since I used a lot of plastic pieces, I decided to use a plastic primer spray paint first. I masked the metal portions because I wasn't sure how well plastic primer would work on non-plastic parts. I masked the business end of the cake decorating tip so the semi-translucent white plastic would light up when the death ray was activated.
I couldn't easily and quickly mask the PVC support, so to save time I decided not to prime it. As it turned out, that wasn't an issue for PVC. However, in general I've found it's a good practice to prime plastic with something like Krylon Fusion.
After masking the pieces, I used a cloth with denatured alcohol to clean the pieces for painting.
I primed the plastic, waiting 10-15 minutes and flipping everything to get both sides.
After priming the plastic, I used Krylon's stone texture paint to add some texture for the weathering that will come later. I didn't completely coat the pieces - not even close. I just dusted the parts to give minimal texture.
Next, everything got a couple of quick coats of Krylon copper spray paint. This covered really well and left a brilliant copper finish - too brilliant for a well-used death ray. Some weathering would definitely be needed.
The techniques I used to weather the prop are described in detail in an excellent YouTube video, Steampunk Painting Techniques: Copper by user It's A Trap! I'll describe the steps, but the video does a much better job - and has moving pictures ;)
After a couple of coats with too-shiny copper spray paint, I dusted the pieces with dark brown spray paint - not to coat, just to dull the copper. I held the spray can 20-25" away and just sprayed a few quick bursts from each direction. You don't want anybody to notice the brown, you just want to tone down the copper shine and darken the pieces slightly. The fifth photo shows the subtle difference compared to the previous photo.
Still, the shiny copper shows through. Prepare an acrylic wash and use it to paint the entire prop. The wash is simply a dab of black acrylic paint and water. Add water to thin it to the viscosity of water. If you can paint newsprint and still read it perfectly well, the wash should be just about right. If the wash beads on the surface of the prop, add a tiny drop of dish soap as a surfactant to reduce surface tension so the wash will flow. You want it to flow into all the nooks and crevices. When the water dries, the wash will have darkened the copper overall and collected in the details enhancing the illusion of age. You can dab at the wash with a dry cloth if you want to reduce the darkening effect, but still have contrast in the textures.
Finally, I mixed together a light green acrylic paint to simulate verdigris from corrosion. I used something like one part dark green paint to two parts titanium white. This helps break up the monochromatic copper tone covering the whole piece. If I'd had time I would have also painted silver accents like the rims at the top of the tank. It would be more realistic if the piece appeared to be made from more than one type of metal.
Step 4: Final Assembly
At this point I was completely out of time, so I threw together some mismatched leather straps with hot glue and adhesive velcro. It's meant to strap to my arm, the tanks on my upper arm and the ray gun on my forearm. I would have loved to have spent more time on the straps, using brass snaps or buckles, but it didn't work out that way.
Finally, I drilled a hole in the light saber and epoxied the corrugated tube.
Done! You can see from the pictures that it looks pretty good when it's illuminated - even better in the darkness of a Halloween party.