There are a great many iconic album covers. One that has stuck in my mind for decades is the cover of the album ‘The Division Bell’ by Pink Floyd. When it came to deciding what to make my girlfriend’s father, a devoted prog rock fan, for his birthday, a miniature replica of the iconic heads from the album cover sprang to mind.
As with most of my projects, I wanted try something I’d not tried before (at least, not successfully!). That thing was cold-casting resin with a metal powder to get a true metallic effect rather than having to fake it with paint (although that was my backup if plan A failed). I also knew that I wasn’t going to be able to 3D print the panel lines into the model – not in a way that would allow me to sand them smooth enough to remove the inevitable print layer lines, even if they were printed at the highest resolution I could, so I knew that I would have to make at least two moulds and hand carve the panel lines into a resin blank. I’m using a Dremel 3D40 printer, printing in PLA, and as I’ve used it for a couple of years now, I’ve got a fairly good idea of what it can and can’t do, although it does still surprise me.
Modelling and Printing the Head
First things first – I had to model the head. I decided early on that I didn’t want to model two separate heads as they are supposed to be identical, so I fired up 3DS Max (my application of choice) and got to work. Finding references proved to be a little harder. The album cover is iconic, and there are lots of nice versions of it around the web BUT it obviously only shows the heads from one angle. To make a a 3D version I needed to find some other views of the sculptures. Luckily Aden Hynes Sculpture Studios had uploaded a video to their Youtube channel of the creation of a pair of 8ft fibreglass replicas of the original heads, so I was able to get some other angles from there – although their versions were flat on the back – plus just eyeballing it to see what looked and felt right.
Once I was happy with the model I exported it as an OBJ, ran it through Meshmixer to make sure it was watertight – Boolean operations in 3DS Max are a bit hit and miss sometimes and can cause weird geometry which doesn’t necessarily matter digitally, but 3D printers and slicing software tends to cry when it encounters such things. I also scaled the model to 150mm tall – the maximum my printer can print on the z-axis.
I ran it through Simplify3D and exported it to the printer. Due to the overhang of the nose and the eye sockets there would have to be some support material, but I figured that these areas would be sufficiently hidden so they wouldn’t matter too much when it came to finishing. Due to time constraints, I couldn’t print the model at .1mm layer height (the highest resolution on the printer) and had to go with the standard .2mm instead. As the heads were relatively flat, and I was going to be casting at least one resin blank to carve in the panel lines, I could do any additional sanding at that stage as resin is far easier to sand than PLA.
About 10 hours later the print was complete and I hit the first issue – while the printer can print objects to 150mm tall, it is the upper limit of the z-axis, and due to some mechanical weirdness, the Dremel moves the build plate up slightly after it has finished printing when it is at this limit, so while the print finished without any errors at all, the printer then helpfully embedded the still hot nozzle into the top of the head, making it quite difficult to actually remove the build plate, let alone the print! After a bit of fiddling, I managed to get it out with minimal damage (other than the hole in the top). After removing the support material I also discovered that the eye that I had modelled in place had not printed particularly well so I clipped that out so it could be a problem for future me to have to deal with.
Finishing the Print and Making the First Mould
With most of my 3D prints my first port of call is a pass with some 100 grit sandpaper to reduce as many of the layer lines as possible. After that I give it a couple of good coats of filler primer, then hit it again with the 100 grit. After this pass I filled any problem areas (I use ‘Fine Surface Polyfiller‘, which is probably the wrong stuff to use for these things, but I’ve not had any issues so far, and it is far, far cheaper and safer than bondo, or similar) and sanded them down as well. I gave the whole thing a few more sanding passes, moving up to about 400 grit. I wasn’t too worried about any remaining print lines at this point as I was going to cast a resin blank to do additional work on anyway.
Once I was happy with the surface finish it was time to make a mould. I knew that as it had a hole straight through at the eye I couldn’t do a simple one part mould and would have to make a two-part. This wasn’t a problem, as I’d done them a couple of times before – this time my concern was the time it took the silicone I was using to cure – almost 24 hours. Given my time constraints – his birthday was in three days, and I had to go to work as well, I decided to bite the bullet and pay out for some proper Smooth-On silicone, which cost considerably more than the stuff that I usually use, but most importantly – it cured in 4 hours, rather than nearly 24. For those interested, I went with a 1 gallon tub of MoldMax 14NV, which is tin (condensation) cure, doesn’t need a vacuum chamber and mixes at a 100:10 ratio, so it is super easy to work out the splits. The other great thing I discovered is that the Smooth-On website has a whole bunch of calculators to work out how much silicone you need to use based on the size of the mould box, the size of the piece and the type of silicone you are using. NO MORE GUESSING! It also has calculators for working out how much resin you’d need for the eventual casting among other things.
Measuring the mould box and working out the volume of that wasn’t an issue, and in MeshMixer you can find out the volume of the 3D model in cubic millimetres (click on the ‘Analysis’ button, then choose ‘Stability’ from the menu). A quick conversion through Google gave me the amount in cubic inches, which is what the calculator was asking for.
I plugged in the numbers, and as I was making a two-part mould, divided the result by two to get the final result. I used some clay to support the head and clay-ed up around the rest of the model to get ready to pour the first half of the mould. I wasn’t too bothered with the seam being particularly neat on this one as it was essentially a junk mould, so I wasn’t overly careful about the edges. I built the mould box out of some Foamex (Sintra, for Americans and other aliens) and hot glued all the joins and stuck it down to a piece of MDF. Once the first half of the mould had cured, I removed the walls, cleaned away the clay, rebuilt the box, sprayed everything liberally with mould-release (such an important step, that I only forget about 50% of the time!) and poured the second half.
The First Casting & Carving the Lines
After the other side had cured, I pulled the mould apart – I’m always a bit nervous about this step as I didn’t want to have to attack it with a scalpel. Fortunately it came apart fine and I could remove the master. I made a couple of foamex plates that I could put on the front and back of the mould and cocooned it in rubber bands. I wasn’t using a Smooth-On resin as I already had some of the other stuff (available here), but given its cure time and viscosity, I figured it was quite similar to the SmoothCast 300, so used that with the calculator on the website, which worked out fine. I also tinted the resin grey using some black translucent resin tinting pigment (you’re supposed to use this with the water clear resin to give it a tint, but I’ve found it works fine with the opaque resin that I’m using as well) – the resin cures white normally, and significantly lightens any tint added to it, so I wanted to see how much tint I’d need to get the right-ish grey for the metallic finish.
The casting came out a bit lighter than I wanted, but it gave me a good starting point for the final casts. I gave the model a few sanding passes to get the majority of the remaining layer lines and drew on the panel lines with a pencil, trying to match the front and back as closely as I could. Once I’d done that I carved them into the surface using needle files, trying to keep them as straight as possible (at which I was only partially successful…). With that done, it was time to go through the moulding process again. I was a bit more careful about the join line this time, so I could get the two halves of the mould to meet as neatly as possible (again, I was only partially successful. Need to up my clay-ing up game…).
When that was ready, I did a quick test cast to make sure the details had come out OK, and then it was time to do the cold-cast process. There are a couple of ways that this is done – some places say you should just mix the powder in with the resin and that will be enough, but I’ve not had any success doing it that way in the past, so I went with the method that Bill & Britt at Punished Props Academy use, which is to dust the mould with the powder and mix whatever is left over into the resin. As an additional step I also added two small spoonfuls of the powder to the resin as well, just to make sure. I poured the resin and then waited nervously for the 15 minutes or so that it would take to cure enough to be removed. I could probably have waited longer, but I’m impatient.
When I peeled open the mould I could tell that something had gone better than expected – the casting, rather than being the flat grey I had been getting previously when I tried cold-casting things, actually had a slight metallic sheen to it. It was also very hot still (curse my impatience!). I let it cool a bit and then buffed it with some steel wool. The result was, to me, nothing short of amazing. I’d seen cold-casting videos, I’d seen photos of it, but up to this point I’d never actually managed to get anything remotely like it. So that was nice. It still had a bit of an ugly seam line which I couldn’t remove, as too much sanding with cold-casting removes the metallic skin, so I had to buff it as much as I could. Still, it came out amazingly better than I expected. I prepared the mould again and cast another, which thankfully came out just as well.
To add a bit more depth and weathering to the metal I painted over all the joint areas with black acrylic paint, quickly wiping it off and re-buffing it with the steel wool so it only stayed in the recesses. The effect was quite subtle, but it added quite a lot of the depth that I wanted. Unfortunately it also served to highlight some of the layer lines that I’d missed, but in the long run, I could live with that. If I make some more in future I might cast a blank and re-sand it to completely get rid of them.
Dealing with the Eyes
Now on to the eyes. The original eyes I modelled as part of the printable object didn’t survive the printing process, so I needed to make some new ones. I printed out a couple of cylinders to the right size, with 100% infill, and carefully drilled a hole through the middle of them. By carefully, I mean I eyeballed it. Quite badly in one case. I had some 2mm styrene rod that I was going to mount them on anyway so with the hole in one of them that was definitely not in the centre, I glued a bit of the rod in the hole, clipped off the excess and re-drilled it, taking a bit more care this time. With that done I threaded both eyes onto the styrene and cut the rods very roughly to the right length. I knew I’d have to tweak it a bit to get it to fit properly in the eye-socket, so I left myself with quite a lot of excess to play with. I painted them with Citadel paints as I had them in roughly the right colours.
To get them to stick in the right place in the eye socket, I couldn’t drill any holes, so I was going to have to surface glue them (not at all ideal, but they weren’t going to be handled much). I trimmed the styrene rod to as close as I could possibly get it to the size of the eye socket, then laid the head on its back and put supported the eye with some clay. I dribbled a bit of CA glue onto the joint and hit it quickly with the accelerator spray, so that none of the glue would run out the other side. It seemed to work, and they stayed where I wanted them. I had to push out and re-glue one of them as it wasn’t quite in the right place.
The final stage was to mount them onto a base board that I picked up from my local hobby shop for a few pounds. I also added a bit of wire with four beads between the mouths (I wasn’t sure about this step – the album cover has four lights between the mouths and I wasn’t 100% sure if this was important, but it felt right. I initially toyed with making them actual LEDs, but I didn’t have a) enough time, or b) any LEDs small enough.
Wrapping it up
While I am very happy with how these turned out, there are a few things that I would do differently, if I make another set:
- I’d be more careful with my mould making. The mould line around the outside edge of these casts is quite ugly, and due to the nature of cold-casting I couldn’t satisfactorily remove it. There is always going to be a bit of flashing with two part moulds, but I could have made the line neater. Alternatively I could have carved in a panel line around the perimeter which would have given me a straight line to clay to, and would have potentially hidden the mould line a bit better.
- Given more time and money I would have picked a better base for the heads – The one I got was very cheap plywood, and while most of the nastiness was hidden by the black paint I used to cover it, it still feels a bit cheap and nasty.
- It would be nice to be able to cast the eyes in place. That was my initial plan, but as they didn’t print properly I had to improvise. They don’t need to move, so in hindsight I could have glued the eyes in before I made the second mould, which would have removed the need to glue the eyes in later. My concern with doing that though was that I might trap some air in that area when casting it and cause problems. Also as the eyes aren’t metallic, I wasn’t sure how the powder would affect the paints.
I hope that this write-up has been helpful, interesting and / or informative and I haven’t bored you to death/tears/drink. I am going to try to do more of these for each of my projects as it helps me put into context what I’ve actually achieved.
Until next time….