Introduction: Bas Relief Light Sculpture

This process started as the ultimate way to carve a jack-o-lantern, but other materials can be used to great artistic effect. Carved in bas-relief, the design is only revealed once the material is back-lit.

Step 1: Materials List

What you will need:

1. A pumpkin, or some slightly translucent material.
2. carving tools (if all you've got is a knife, it's going to be hard).
3. light.
4. an image or an idea.

Optional (but recommended)

1. something to project with.
2. markers to transfer your design.
3. a basic graphics program of some kind.

Step 2: Image Selection and Modification

I fielded a lot of questions about image selection at the Makers Faire, and what follows is the best advice I've been able to come up with.

  • use images that have strong directional lighting. You may have more than one source of directional lighting, but very diffuse light is not good. Stronger gradients are better. Camera-mounted flash-photography is bad. Don't pick a simple silhouette, or something front lit. it should be off-angle lighting to emphasize the cognitive dissonance.
  • an image that needs very fine detail for its impact makes the carving very tedious - so avoid extreme subtlety in expression if you're doing portraiture. Pick something that will have punch, even if it is very blurry.
  • I think it's also good to have an image where both the foreground and background of the image have gradients. If the background is always much brighter or darker than the foreground, then your topography won't be interesting. You'll have a plateau or a simple recess that outlines your figure rather than an dynamic interplay of sculptural shapes. (You can fix this in an image you like by messing around in your image editor.)
  • extreme close-ups for portraiture can create interesting and unintuitive topographies where the image jumps out suddenly.
  • at a crazy advanced math level, you'll probably start to be able to see the topographical forms that the sculpture will take based on the light patterns. At this point, you'll want to pick cool-looking topographies that create unintuitive images when viewed from the viewing angle. I wish I could do this better. It really taxes my brain, but it's what I'm trying to get better at.

So, with all that in mind, get your image. Draw something, take a photo, or find something. If you're drawing a blank, google image search can help. pick an adjective and do an image search. Use CoolIris to scan your seach quickly for something that catches your eye.

Now that you have your image, adjust it so that it's easy to interpret into your sculptural topography.
Photoshop, the Gimp, or another graphics program can help quickly reduce the image to something carve-able. You'll want a black and white image with a lot of contrast. Some areas should be washed out (entirely white) other areas should be lost in shadow (totally black) you also want some mid-tones. Use "levels" or "curves" to alter the contrast on your image. Then use "cutout," or "posterize," filters to alter the image. This will create discrete lines from the gradients to guide your carving. You can think of them as topographical isobars. Your goal is to make obvious the light/dark gradients in your image so that you can translate them to height/depth gradients in your carving.

note: if you're carving in something other than a pumpkin, (specifically, something like styrofoam) where you don't want to completely cut through the object, and where you don't have a top "skin" that will create dramatically contrasty blacks, you probably don't want to have an image that is too contrasty. You still want a lot of range, but you want smooth gradients that keep detail in the highlights and dark areas. This is because a solid black area will become an flat-topped plateau in your carving that isn't sculpturally as interesting as a rounded hill or a jagged peak. Take a look at what I'm talking about in the maker's faire styrofoam carving below. It still looks like a block of styrofoam because the shadows got cut off. It would look better if it had rounded peaks rather than a chopped plateau.

Step 3: Carve It.

Before you transfer to pumpkin, make sure that no black or gray area is completely surrounded by white. That would destroy the structural integrity needed to keep your shadows where they need to be. Darken white areas that surround shadows to fix this problem.

Transfer the lines to your pumpkin. I used this tracing projector that I got at a garage sale, but an LCD projector, or an overhead projector would also work. Tracing or transfer paper will work fine if your surface is relatively flat, but I think the effect is much better (and more fun) if you project onto a surface that's not flat. That makes off-angle viewing distort, and the only angle that the image can be viewed from will be in the direction you projected from (also note that your carving should all be done with that angle in mind).

Every area that is white in your image gets cut out completely first. Then you start removing material from areas that are gray. Be careful to leave every black area intact. While you're carving it's very helpful to have a light source behind the carving. A low-wattage light-bulb on a cord is helpful. A good reference copy of the image you're using is also very helpful, because there's almost a cognitive dissonance with this kind of carving. For me the physical shapes and lines carved don't intuitively relate to the final image. it's very helpful to be able to walk away from the pumpkin and see it from a distance while you're carving. I also squint a lot when I do it.

At some point, you'll get to a stage where your image on the pumpkin is starting to look good, and you'll probably find that at different points in the carving process, you've departed somewhat from a linear translation of the original image. My advice: embrace this. Don't try to make the pumpkin look exactly like the image you projected. Adjust lines, think about viewing impact and viewing direction. Make dramatic cutouts, feather your mid-tones in ways that make sense for the pumpkin image. Your original image was a guide to get you started, not something to use to rate your success. Throw it away when you reach 75% completion.

Step 4: Maker Faire Update

At the first Maker Faire I had the opportunity to explain what this is over and over again, and to make some new versions. check

for that update. It has some examples of non-pumpkin carving using this technique, as well as thoughts on the sources of cognitive dissonance that is created in the mind of the viewer.

also this flickr set, if you care to:

Step 5: Halloween 2007 Update

I carved another pumpkin in 2007

(below excerpted from: )

I kinda felt like this was a practice pumpkin in a lot of ways. What would it be like going for a more minimalist twist?

Answer: I think the level of detail and the complication of the forms on earlier attempts actually resulted in a more effective experience.

Drawings of cubes may be classic optical illusions, but I feel that in this case, the viewer's ability to interpret a "normal" cube in multiple formulations (convex, concave, open, closed) in some way over-rides the sense of distorted space. There are other problems, too.

Ask yourself, is the top of this cube open? or reflective? To my eye, it could be either. This ambiguity somehow makes the form less interesting. In the end, this carving does not make you reassess what the source of the lighting is. While it's possible that the top of the cube is a solid reflective surface, the prior knowledge that the pumpkin is lit from within actually pushes you to interpret that the top of the cube is open, even though this means that there's a missing line. It ends up looking almost like a paper bag with a candle in the bottom of it. And that's not such a leap to make from a pumpkin with a candle in the bottom of it.

Hope you enjoyed! now go make something cool, and let me know about it.