Work in Progress: A Dragon's Eyes (part 2)

As of Thursday three weeks ago I had a reasonable reproduction of an original dragon sculpture's face and eyes, but I had only a vague idea of what I was going to do to make the glowing eyes themselves.  It was the eyes after all that I was originally consulted to make not the reproduction of the face (that was a fun side-project that I could alter if necessary).  Dean and Adrienne want vibrant, purple eyes visible from the end of their block, and the inspiration for the modification had been a pair of edge-lit, cat's eyes goggles I had made for my wife as a costume piece.

The existing eyes of the dragon sculpture have a pronounced hemispherical curve, and I decided to maintain that shape as much as possible.  Simply carving the eyes out and replacing them with pieces of flat Plexiglas would certainly accomplish the desired effect, but making the eyes look alive will require keeping the corneal curve.  The best possible result I thought would involve making a complex eye out of three differently shaped components lit in different ways.  I came up with the idea of a curved, clear cornea (replacing the existing eye) sitting on top of a flat, etched piece of edge-lit Plexiglas (etched to resemble an iris) backed by a third, curved piece of clear plastic or glass lit directly from behind by a differently colored LED (amber or red as the backing color behind the purple iris) to look like reflection off a retina.

I don't posses the equipment to grind a lens.  What I needed therefore was to find something (either glass or a clear polymer) that already had the desired curve.  That meant I needed to know what the curve of the existing eye is.  I assumed that the curve matched the surface of a sphere.  I took a couple measurements, used some basic geometry, and I estimated that the eyeballs of the dragon would be about 1.5 inches in diameter.  Roughly the size of a ping pong ball.  That's convenient.

As I was wandering aimlessly through a hobby store looking for a clear object with the shape I needed I happened to notice a package of clear epoxy resin on a shelf.  It was packaged in two parts like the polyurethane I'd used to reproduce the dragon's face, and that made me think about the possibility of making a lens with the curve I wanted.  Over the next few days I experimented with differently shaped molds and clear, pourable media (clear epoxy, acrylic cement, jeweler's resin, and even cyanoacrylate glue).  I had the best results using an oogru mold I took of a ping pong ball (again, convenient) with jeweler's resin.  This produced a clear, hemispherical object similar to a lens.

Various lenses and molds in the experimenting phase of my design.

Jeweler's resin is a two-part, viscous resin that takes at least 24 hours to cure.  This extended cure time prevents excessive heat production (which can cause cloudiness and discoloration I discovered with the clear epoxy) and gives any bubbles in the mix time to rise to the surface.  The result is an optically clear plastic (unless you add dyes) with an amazingly durable and scratch resistant surface.  It can be poured over a table or counter (for example) to create a laminate or into a mold (that may or may not contain other items, encasing them in the resin) to make jewelery or other plastic parts.  The surface exposed to air is amazingly clear, but the surface in contact with the mold takes the texture of the mold.  Since neither the ping pong ball nor the oogru out of which I made the mold are perfectly smooth the resulting lens when unmolded had a hazy surface that appeared to have been frosted.  The curve was perfect, but I couldn't see anything through the rough surface.

I spent another day contemplating techniques that I could use to polish the surface of the lens to make it crystal clear.  I was about to begin testing the resin's response to fire-polishing or using solvents to smooth the surface when I remembered that the flat part of the lens (the part that had been exposed to air while the resin cured) was already smooth and clear without polishing.  I wondered what would happen if I layered the resin.  Would there be a distinct difference between layers, or would old and new layers bond seamlessly?

The top lens is right out of the mold. 
The bottom lens is polished by
adding another layer of resin.

I mixed up another batch of resin, dabbed a couple drops of liquid resin on the top of the dome of the lens (as it rested on the flat surface on a table), and smoothed it carefully over the entire frosted surface.  The rest of the batch went into the same mold from which the first lens came just in case I ruined the one I was working on.  I had hoped that the viscosity of the liquid resin would keep enough of it from simply running off the sides that it would leave a sufficiently thick coat, but with a cure time of 24 hours all I could do was wait and see.  Much to my delight it worked almost perfectly!  Some larger imperfections on the surface of the original lens were still visible, but for the most part the new resin had cured to a glass-smooth finish.  I made new molds taking extreme care to eliminate as many imperfections in the mold as possible, and I poured new resin lenses.

The scariest damn drill bit EVER!

As the new lenses cured I set to work making the next layer of the eye: the iris.  I have a drill bit specifically made for cutting perfect circles.  It's the scariest damn thing I've ever seen attached to my drill press.  It looks like parts are going to come flying off at close to sonic speed at any moment.  I take extensive safety measures each time I use it just in case one of the parts of the bit does come flying off.  It cuts neat circles in Plexiglas though, and that's what I use it for.  I cut a pair of one-and-a-half inch disks out of quarter-inch thick acrylic and drilled holes in the edges on opposite sides to accommodate a pair of 5mm LEDs.  Etching and abrading the disks to resemble a slit-pupil iris was an afternoon project since I've done similar work previously (it's just like making the cat's-eyes goggles).  Gluing the LEDs in and wiring them in series with a resistor was accomplished the following afternoon (never power a LED without a resistor in series or you're basically creating a short-circuit). 

The iris disks, front and back.  The front is frosted by abrading with sandpaper, and
 the back is etched with radial lines to give it a three-dimensional appearance.  There
 are holes drilled in the edges top and bottom for the LEDs.

The iris all wired and lit-up.  The UV
 LEDs for some reason are highly visible to the
camera, but not to the naked eye.

The electronic parts stores in town don't have purple LEDs, so I started with ultraviolet LEDs.  Ultraviolet however is invisible to the human eye.  The hints of purple you see when looking at an ultraviolet light are actually a different wavelength entirely "leaking" through.  UV light does have the interesting property of changing its wavelength in response to many surface materials and reflecting back as a very different color (this isn't entirely accurate at the quantum level, but that discussion is a bit too involved for the scope of this project).  Fluorescent colors (a.k.a day-glo or neon) are the most vibrant examples of this effect as can be seen at many nightclubs ("color brightening" fabric detergents and softeners also contain fluorescent compounds).   My idea was to add a surface paint on the back of the acrylic disk that fluoresces purple under a black-light.  This would serve two purposes: first it would convert invisible UV light into a vibrant purple, and second it would block any light coming from behind the iris everywhere except through the pupil (the only part of the disc not painted).  The "retina" I was still planning to make would then be visible only through the slit pupil.

Do you have any idea how difficult it is to find fluorescent purple paint?  For that matter do you have any idea how hard it is to find fluorescent blue paint for mixing with fluorescent red paint (which is easy to find) to make fluorescent purple?  Red, orange, green, and yellow are all readily available.  I searched for a week to find purple.  I was about to give up, and I had even ordered ultra-bright purple LEDs from a supplier in China as a back-up plan.  By luck however I found the only purple pigment (evidently) in existence in the form of a paint intended for use with an airbrush.

With the cornea and iris completed all that was left was the retina (and of course to mount the whole thing).  Compared with the trouble I had been having with the other two components the retina was a breeze.  All I needed was to use one of the spare jeweler's resin lenses with its flat side to the back of the iris component and to shine a red or amber LED from about an inch behind the curved side of the lens.  This creates a watery glow rather than a pinpoint of light.  I used a breadboard to assemble both an amber and a red LED for test purposes.

This is what it looks like completely assembled.  The red LED shining through a convex lens set behind the slit pupil in the iris disk.  I think it looks really amazing, but it's a very complicated arrangement.

Up next: Putting it all together.