So you are lucky enough to have access to a laser cutter? And you want to do something really awesome with it? How about putting your own designs on a piece of chocolate?

In this Instructable, I'll tell you about how I laser etch designs onto chocolate, and the tips and tricks I have found so far.

The most important insight when working with chocolate is that the etching works more by melting and re-settling the top layer of the chocolate than by vaporizing it. This means that the etching is a fundamentally unsubtle process, and also has implications for the resulting colors, the resulting structures, and for handling the chocolate in the middle stages of the process.

Step 1: Pick and Prepare a Picture

First of all, you need a picture to etch onto chocolate. A design.

For the design, don't try to be subtle. Grey shades don't carry particularly well: the most clearly articulated part of etched chocolate is the difference between etched and not etched: different shades will be hard to pick out, if at all possible, in the finished product.

For our running example today, I picked a picture of the Golden Gate Bridge I took a while back. The picture is already in black and white, so we can skip the greyscale conversion: however, I would recommend you do convert your image to greyscale — this gives you more control over what parts of the image are dark or light. However, to emphasize the shape, I used Photoshop's «Posterize» filter to get a more quantized image with very few grey scale steps.

Step 2: Pick and Measure Your Chocolate

You need, in addition to your design, a piece of chocolate to etch onto. You will want the chocolate surface to be reasonably smooth and flat — don't etch onto the side with the manufacturer logo, or onto the squares, but rather on the back side of the bar. This is not only to get a good design canvas, but also because if you try to laser etch out of focus, you increase the risk of “remodeling by laser”: causing fires and destroying your attempt.

Once you have your chocolate picked out — I picked a Ghirardelli extra bitter mini square — you need to make sure you know the dimensions of the chocolate piece, so that you don't etch outside of the actual chocolate piece you want to etch. My pieces work out to 1.7" x 1.7".

Step 3: Layout the Design for the Chocolate

In the design program you use — TechShop SF has CorelDraw to control their laser cutters — setup a page size corresponding to the chocolate size from the last step. Import your image however the design program needs it imported, and add anything else you want in your design here. You are laying out the print job on the chocolate, basically as if it were a page you would print on.

Notice that if your image is light-on-dark, like the jellyfish I experimented with, you may want to invert the image in this step so that the laser only etches the contrasting part, and not the entire background of your image.

Text works well too — but I won't cover it in this Instructable.

Step 4: Laser-etch the Chocolate

It's time for lasering! Hopefully since you have access to a laser-cutter, you will know the fundamentals of how to work with a laser cutter. As a reminder, and an overview for anyone reading this out of curiosity or for a future project once laser cutter access has been acquired, the steps you need to take are:

Setup your design (see previous steps of this Instructable)
Switch the laser cutter on. Check that all ventilation systems are working. Check that the vector plate is mounted properly, and that the tray underneath is empty. Check that the lens is clean, and that the cutter is aligned properly.
Put your chocolate on a tray of some sort: paper plate, piece of cardboard, paper napkin… The laser cutter is most likely used to cut things that aren't chocolate — and you don't want your nice candy to get infused with, say, acrylic fumes.
Put the tray on the vector plate. Try to align it in the top left corner, for simplicity.
Focus the laser cutter.
Setup the printer settings for your control system. Make sure the dimensions of your design match the dimensions inside the Epilog driver dialogue.
Setup the laser cutter settings in the printer dialogue. I use, for most of my chocolate etches, on an Epilog 60W cutter: raster only, 50% speed, 30% power, 400dpi.
Send the print job.
Push “Go” on the laser cutter, and monitor the job until it finishes. For a full size chocolate cake, these settings will be done in roughly 8 minutes. For the Ghirardelli 1.75" x 1.75" mini bars, it takes about 1m30s.
If you want to do double passes, repeat steps 8-9.
Retrieve your chocolate bar carefully. You may want to consider using a spatula, especially if you etch very close to the edge: when you remove the chocolate the etched surface is going to still be molten chocolate.
Let the chocolate solidify in a fridge for a few minutes.

One thing I noticed when preparing this instructable is that chocolate is very forgiving with respect to power settings. I went up to 50% speed, 60% power at 400dpi and not much changed. The more power, the more heat, the bigger part of the chocolate melts; but safety-wise, you can do much as you like here.

Most likely, by cooling the chocolate completely between passes, more passes and higher power will contribute to deeper etched profiles down into the chocolate — but cooling the chocolate between passes will lead to problems putting it back exactly right, to get the registration right and not accidentally etching on a ghost image just barely next to the one you started with.

Step 5: Things to Keep in Mind

This process works by melting and re-solidifying chocolate. You will get a slight height difference, but nowhere near what you may have hoped for.
Pick a design with lots of contrast. Black in your design program will come out reddish on the chocolate. White will come out chocolate brown. Even very light grey comes out more red than brown.
Invert your design if you need to.