That's no moon...
Who hasn't dreamed of owning a half-destroyed battle station made of concrete that functions as a light? Anyone? Okay, so it's not exactly practical but it was fun to try to something new.
I saw a transparent plastic sphere at a local shop and immediately thought of making a Death Star pendant lamp out of concrete. This was sparked by looking at a whole bunch of helpful instructables about how to make concrete pendant lights. I've also seen instructions about how to make a Hollow Concrete Sphere and about passing light using optical fibres. I wanted to combine those three concepts whilst playing around with concrete/cement.
Making hollow spheres out of concrete usually involves building layers onto an inflatable ball. I wanted to build it the wrong way around - to have a pattern on the outside. It didn't seem like it would be particularly easy to do but I wanted to try anyway..
This is my first experiment with using cement-based products in this way, so please let me know if you have any tips on how to do it better or if you have any comments!
Step 1: Materials and Tools
Here are some of the stuff I used:
- Transparent Plastic Sphere: To use as the mould. I found a cheap ball for hamsters (~16cm diameter) that splits in half and has a handy access hole. You can usually find plastic balls - I had a similar size one that was briefly full of chocolate pieces...
- Transparent Silicone Sealant: to make the window/see-through sections.
- Fiba Tape: Alkali-resistant tape to add tensile strength to concrete. The grey grid pattern shown underneath the transparent sections should also make it look a bit like the building structure.
- Concrete, Grout: to hold it all together and fill gaps.
- Craft Foam: for marking trench-ish shapes. I've tried using oil-based clay but found that stuff hard to remove from the concrete once set.
- Plastic Fibre Optic Cable: I got this from a cheap light toy. If the lengths are short and straight, you can use clear fishing line too although it won't be as bright.
- Pendant Light Socket with bulb: This lamp will get hot so we should use LED bulb or similar that doesn't generate a lot of heat.
- Hook: Hanging heavy things from electrical cable is not idea. Use hooks to take the weight. A threaded tube and nuts would have been better but I couldn't find any locally.
- Safety Gear: Nitrite gloves, eye protection, and mask for handling cement/concrete
- Drill & Bit (1.5mm) & Hole-saw bit (54mm): To make holes. Also to cut out a circle to make the super-laser part.
- Hot-glue & Gun: Always handy to have.
- PVA glue & mold release: To seal the foam. For the release, I used a bike chain lubricant spray though some other oils should be fine.
- Various buckets, bowls, cups
Step 2: The Basic Shape
It's easier to work on the inside of the sphere if it's in halves. So first I split the ball...well actually, I dropped it accidentally and it fell apart. I took the opportunity to rip off the plastic tabs holding the sphere together otherwise it would've been annoying to take it apart later. My shell came with handy grid lines on the shell - you can always draw them if they're missing to help with the layout.
I drilled the big hole a little above the equator for the super-laser. I duct-taped both inside and outside to stop the plastic from shattering/splitting. Using a hole-saw bit means that you can reuse the circle of plastic as the super-laser. This circular offcut was flipped over and hot-glued into place.
Sketching the damage outlines
After searching for some reference pictures for Death Star 2 from Star Wars Episode VI, I sketched out with a sharpie where the damaged sections should be. There's a line of damage that runs across the entire front (below the super-laser) and the whole top-right and bottom-right sections are deeply damaged, concave and exposed. The edge of these damaged areas show the lattice structure of the space station but the middle be indented.
Deep damage sections
I could create the concave sections in the Death Star by adding bumps in the mold. I dumped a whole lot of hot-glue into the where I drew the deep-damage sections until it was ~1cm thick. I had to do this in several few stages - wait for the glue to cool before adding the next layer to get more height.
Step 3: Adding Some Detail
This is tedious to have to do but needed to add little point-lights on the Death Star surface.
It'd be great if we can cement the optical fibres into the Death Star. However, fibre optic cables (even the plastic ones) snap, break and pull out easily. It might not matter if I used an actual mold (e.g. a ball within a ball) and poured the concrete in...but I was going to be slapping a concrete mix onto the inside of a ball. So I pre-drill the holes and use craft foam to cover them. Then I'll remake the holes with pins after the concrete has been added.
I used a 1.5mm drill bit to drill a bunch of holes on the sphere. The grid markings on the surface of the sphere was handy to follow. Since the fibres are around 0.5mm, this hole should be big enough. I kept drilling until I got bored - which wasn't long.
Add trench / panels
I had some A4 sheets of black craft foam which I cut into strips of various widths (2mm, 5mm, etc). I then glued (with contact adhesive) these on the inside of the sphere over where the holes were. I worked on the top and bottom halves separately, adding the latitude (horizontal) foam strips before adding the shorter vertical strips. I also added random strips, rectangles, and other shapes as I went along.
Note that there's a slightly thicker section (~6mm) that runs horizontally near the top of the sphere.
I glued a narrow piece (~2mm) of foam onto a wider piece (~12mm) for the central equator trench. The two hemispheres were then joined together using four small dabs of hot-glue, and the equator foam glued into place.
For the super-laser a ring of foam the size of the circle was cut and attached. For the inner piece, I pushed various circular objects (bottle caps, cups, etc) into a disc of foam to make marks. I then cut random shapes out along the arc segments and glued it in place.
Sealing the foam
Heating up foam causes the surface to fuse together and helps (a little) to help seal it - I used a heat gun to do this quickly. Foam would seal better if we use something like rubberised paint spray but we need to be able to see into the sphere. So, I then coated the foam using a 50/50 diluted PVA glue/water mix.
Once the PVA is dry, we need to cover the surface with a release agent that will help the concrete / silicone to separate from the ball. It's easy to forget to do this...but is necessary to avoid headaches later. I've read that a mineral oil / vegetable oil mix works well as a release agent but haven't tried it. I had some bicycle chain lubricant spray nearby so I used that - hopefully it'll work out...
Step 4: Add Transparent Bits
I wanted to have transparent sections in the lamp that let out some light as well as representing the damaged parts of the death star. I thought about using hot glue for its strength but the heat would've damaged and fused the craft foam. It might be possible to use lower temperature glue but I didn't have any to hand. Let me know if you can think of other materials that could be used!
What I decided to use was transparent silicone sealant. Silicone usually takes forever to cure and I don't have the patience to apply thin layers. To get a faster cure time, I used the mold making technique of kneading the silicone in glycerin-rich soapy water. Speeding up the cure time makes the finished silicone slightly cloudy but much much easier to shape and push into place.
Tape it up
Take strips of the Fiba-tape (each one approximately the length of the longitude) and place them vertically, overlapping slightly. I used more strips than might've been needed because I wasn't sure how thick I was going to make the walls. To preserve the effect of the Death Star damage, the tape should be oriented so that the grids form vertical / horizontal lines (i.e. instead of diagonally).
The closer the tape is to the surface of the shell, the more visible it will be when the light shines through it. I didn't cover the deep-damages sections (areas with the hot-glue mounds) with tape yet.
Note that these are meant to be self-adhesive but it didn't stick too well because of the oil I'd sprayed over the surface.
I prepared about 1/3 tube of silicone in the soapy water and covered over the damage section outlines. It was probably around 1-2cm thick. I was wary that making it too thin would weaken it but making it too thick would stop the light getting through.
The tape will force the silicone to form weird grid patterns unless you really push it into the gaps. To get a cleaner boundaries, I pushed the silicone from the centre of the mound outwards.
Concrete probably wouldn't stick to the silicone securely. So I added some more Fibatape over the silicone parts so that the concrete would have something better to grab onto.
Now we need to wait for this stuff to cure (harden) which would depend on a bunch of stuff like how warm it is, and how it was mixed. I've had some types of silicone take forever to cure, so it's a good idea to check using a small sample first.
Step 5: Add Walls
The next step is to prepare your favourite cement mix. Cement is not good for your health - I made sure to wear goggles, a mask, nitrite gloves, and did all the mixing outside.
Note: This would've been a really good time to fit a threaded tube where the electrical cable can pass through. I couldn't source these tubes locally so decided to leave it for later.
Filling the walls
The spare bag of concrete I had to hand was quite course and I wanted to use a finer aggregate (smoother) mix to avoid squishing the foam and to get better details. Luckily, I had some leftover quickset grey floor tile adhesive that needed to be used (similar to 'thinset'?). This is a fairly small sphere, so hopefully it should hold together with just that and the mesh. For larger pieces, we might need to use a stronger concrete mix (or maybe even a lightweight cement/perlite/sand mix).
I loosely followed the instructions on the bag and got a consistency similar to creamy mashed potatoes. I had to work fast so used the back of a table spoon to spread this stuff onto the sphere whilst trying to avoid the silicone layers. Like with the silicone, I looked to see where there were gaps and pushed from the inside to squeeze the stuff through the tape mesh.
It was a pain to use because it's really sticky and sets quickly...but on a positive note, it holds together well and sets quickly. Once I'd finished cursing and thought that the coverage was even enough (1cm-1.5cm thick), I moved onto the pins.
Making holes (again)
Where the predrilled holes were, I pushed dressmaker pins through the craft foam and the cement. This is obviously easier to do whilst the cement is still wet. I didn't push the pins in complete so I could pull them out more easily.
Note: It's probably better to insert optical fibres at this point once craft foam was pierced with the pin (so it fuses with the cement). However, I went to have a cup of tea and take a break from all these holes...
Step 6: Release the Ball
When the cement had gained enough strength to be handled (~6 hours for my mix), I removed all the pins with pliers. If some pins were stuck I pushed them in a little before pulling.
Note: How long you have to leave it before taking it out really depends on the cement and mix you use. If it still looks dark and wet, wait some more to avoid breaking it while releasing. The packaging should give a guide about strengthening times.
Remove the shell
I chipped off the bits of hot-glue that held the shell together and attempted to remove the plastic shell. I used a flat-headed screwdriver to ease the shell away without cracking the Death Star. The shell came apart in large chunks but some of the plastic snapped and shattered. Given the bits of plastic flying about, it's probably a good idea to wear gloves and eye protection.
Annoyingly, after the shell was taken off I noticed that there were parts where the silicone or adhesive hadn't reached. I thought I'd put back the foam to retain the shapes and fill this using a dark grey grout. I mixed up some floor (sanded) grout and filled the larger voids, wiping it level with a damp sponge. Once the grout had dried, I took out all the foam.
Fix the optical fibres
I cut a bunch of optical fibres (from a cheap led lamp thing) into lengths of around 4cm - longer is better because we can trim them later. I've read that some glues (e.g. super glue) can heat the fibres and damage them. I added a dab of wood glue on the each hole and pushed the fibres through. Having a light inside the sphere can help see where the unfilled holes are.
Once fixed, I shortened the exposed fibres using nail clippers so that they're less likely to be pulled out whilst grouting.
Fill in the trenches
I had some light grey tile grout which I wanted to use to fill in most of the trenches. Before grouting, I wrapped a thin strip of craft foam around the equator so that I could fill this later using a darker colour. For the grouting, mix according to the instructions on the packet and apply, wiping away the parts.
Step 7: Light It Up!
As a quick test, I drilled a 32mm hole in the top and secured a SES light fitting from a broken table lamp. Because the lamp shade is smallish, I used an LED bulb to stop it overheating. The lamp isn't too heavy but I'll need a better way to fix this before I'd leave it hanging up anywhere...though I can't imagine which room I'd hang this in...
I still need to fill the central trench, clean up the colours and sort out the fixings, but I think this experiment generally turned out ok. If I were to make this again, I'd probably use an enclosed mold (maybe an inner and outer ball) and pour the concrete instead. I'd try to fix the optical fibres in one and avoid all those holes as well...
Anyway, thanks for reading!