Price: $20 at most (if you are buying the ink)
Time: < 1 hour per cork
What you will need:
Step 1: Making Stencils
In this step we will be tracing out paper stencils that we will tape onto the cork and use as a guide when inscribing the cork with ink.
1. Take a cork, place it on your sheet of paper, and trace its edge with your pencil so you have a circle on the page. This will show you what your maximum size is for your image. Do this several times: once for each cork you plan to inscribe and a few extras for drawing mistakes.
2. (Optional) If you don't have an exact picture of what you want to inscribe in your mind, look up the subject you want to inscribe online - I suggest searching for black and white tattoo designs of that image because the styling of tattoos transfers well to what we're doing. Additionally, try to find images that don't have very close spaced dark areas or very large dark areas - they will be more difficult to inscribe in the cork.
3. Based on the image you've looked up online or your mental picture, draw that image into the circles you created on the page in step 1. Try to keep them away from the edge of the circle so that when you're carving the edge of the cork will not break off. You should get a result similar to the image above.
4. Photocopy the images at least once - you'll be cutting through the stencils, so if you make a mistake in inscribing the image and need to start over, you will want a fresh stencil.
5. Cut out the stencil images you will be using.
Step 2: Tracing the Stencil Onto the Cork
Next, we will be transferring the lines to the cork by cutting them out through the stencil, much like carving a Halloween pumpkin. Knife cuts don't leave much of a visible mark on cork, so mistakes won't show up. Therefore, its easiest to do this as a dry run without ink and then ink the correct lines once they're already in the cork. Doing this makes the inking much easier and neater because both the knife and the ink will tend to stay in the line you've already cut.
1. Tape the stencil onto the cork. Tape it in many places because once you cut through the stencil, you may have cut through some of the paper's connections to the tape.
2. Take you're X-Acto knife and diligently cut out the lines. The cuts do not need to be tremendously deep. Cutting shapes (non-lines) may require many cuts and some amount of angling the knife. The stencil may get fairly trashed during the cutting, especially if you have many shapes in close proximity. If you really need to, you can take off the original stencil and attach one of the photocopies, but keep in mind that it is very hard to line it up exactly right again.
Step 3: Inking the Lines
(Apologies for the blurry image of the final inked cork in this step)
1. Unless the stencil really needs to be replaced, then use the same stencil that you have already cut through for this step (see the caution at the end of the tracing the stencil section).
2. Pour out some of your ink, and use your knife like a quill - that is, dip it into the ink and then retrace the lines that you have already cut into the cork. The paper absorbs some of the excess ink and therefore helps you avoid blotting the cork, but to further sidestep this issue, use only a small amount of ink at a time as you trace the lines. For shapes, however, you may want to load the knife quite heavily with ink.
3. Once you've inked all the lines, you can detach the stencil and take a look at your handiwork.
Step 4: Finished Product!
(Optional) If you happen to be decorating jars for this project and should those jars happen to have contents that you need to label, I would add that you can attach labels to the jar by buying some shoelaces for a man's dress shoe (a couple bucks at a local CVS or similar pharmacy) and tying the labels onto the jar with those.
Otherwise, congratulations, you're done! I hope you enjoyed the project and that you and/or your gift recipient will be pleased with the result.