Introduction: How to Make Banana Oxidation Art/ How to Tattoo a Banana

About: My name is Jason Poel Smith. In my free time, I am an Inventor, Maker, Hacker, Tinker, and all around Mad Genius

We've all seen bananas turn brown. In this project I am going to show you how to use this browning process to intentionally cause certain points on a banana peel to brown prematurely. This lets you make pictures on the banana peel using only a small needle. When done properly, it doesn't affect the edible part of the banana, so you can still eat it later. This is a great arts and crafts project to add a little fun to your packed lunches.

Step 1: Background: Why Bananas Turn Brown

So why do bananas turn brown? Here is some of the chemistry for those who are interested. 

It all has to do with a series of chemical reactions that take place as the banana ripens. This process is called enzymatic browning. As the banana ripens, the membranes in the cell start to weaken. This lets the phenolic compounds in the cell's vacuole come in contact with enzymes like polyphenol oxidase. The enzymes cause the phenolic compounds to quickly oxidize. This reaction produces melanin which gives the ripening banana its brown spots.

If we manually rupture the cell membranes, we can cause this process to take place quickly in specific locations. Puncturing the banana peel with a needle will create a well defined brown dot in a matter of minutes. By making a lot of dots we can draw a picture on the banana peel.

TL;DR  Puncturing or bruising the skin releases chemicals that make it turn brown.

Step 2: Selecting the Proper Materials

To make this project you will need three things:
  • A reference picture
  • A banana
  • A sharp tool for marking on the banana

First, if you're like me and can't draw to save your life, you'll want to select a reference picture. I am using The Cat in the Hat as it is a simple image that is easy to illustrate. However, you can feel free to select pictures that are more complex. Detailed pictures such as the examples shown in the intro step took me several hours to finish. It also helps if the picture is proportioned so that it can at least somewhat fit on a banana. Long rectangular pictures will fit better than square pictures.  With most pictures, you will probably need to crop the edges a little.

When selecting a banana it is important to keep in mind how the peel changes throughout its ripening process. The greener the banana is, the firmer its cell membranes are. That means that they are less likely to rupture from simple pressure. As a result, when the cell is punctured, the chemicals do not bleed as much. This creates smaller more well defined dots. Riper bananas with weaker membranes will bleed more and will create larger dots with softer edges. For pictures with small well defined lines, I recommend a banana that is either a 4 or a 5 on the ripeness scale pictured. For pictures with thicker or blurred lines, I recommend a banana that is closer to a 6 on the scale.

The marking tool that you select is again determined by the kinds of lines that you want to make for your picture. Any sharp object can work, but as you might expect, each tool creates a slightly different mark. Smaller needles (like sewing needles) create small light dots. Larger needles (like thumbtacks) make larger darker dots. Regardless of what sharp object you choose, you may wish to modify it slightly to make it easier to handle. For instance, something as small as a sewing needle can be difficult to work with. So I inserted it into the end of a 0.5 mm mechanical pencil. This made it a lot more convenient to use.

Step 3: Apply the Stencil

If you are not a great freehand artist, I recommend starting with a stencil. Print out a copy of your picture scaled to the size of your banana. Then cut it out and line it up with your banana. You may need to trim it so that it will lie flat. Once you are happy with the positioning, tape down the edges. A little creasing or folding of the paper is ok as long as it doesn't distort the image too badly.

Step 4: Create a Dot Outline

The first step in applying your image is to create a rough outline of all the major edges. On a given line, use your needle to pierce through the paper and into the banana peel. Try to make the puncture as shallow as possible. Repeat this all along the line. Try to keep the dots close together (no more than 1 mm apart).

Your hand will probably get tired after a while. This is the thing that everyone hates about pointillism. Try to complete whole lines or sections before taking a break. Otherwise a line may to look uneven if certain parts are older and more developed than others.

After you have traced over all the major lines, you can remove the paper stencil. If all went well, there should be a faint dot outline of your image on the banana peel.

Step 5: Connect the Dots to Make a Solid Outline

Now it's time to play connect the dots. Go back over each line and fill in all the spaces by adding more dots until it looks like a solid line.

If at this point you and your hand are completely fed up with making dots, you can take a shortcut and connect the dots by just cutting the lines with either a knife or by dragging your needle across the surfaces so that it breaks the skin. This doesn't gives you quite as much control over the line shape but it is a lot faster and easier.

Step 6: Apply Shading

After you have finished defining all the solid lines, it is time to add shading. When working with a banana peel the most useful shading techniques are stipplinghatching, and smooth shading.

Stippling: Creates shading by varying the density of dots. The closer the dots are to each other, the darker the area appears. This technique offers the most control but is the most time consuming. To create large dots, make shallow punctures in the skin as you did in the previous steps. To create smaller and lighter dots, hold the needle at a shallow angle and use your finger to repeatedly tap it against the surface. You may need to repeat this process several times to get the area dark enough.

Hatching: Creates shading by varying the density of parallel lines. The closer the lines are together, the darker it appears. This can be done with lines in a single direction (basic hatching), lines that intersect at an angle (crosshatching), or lines that follow the curve of the object (contour hatching). Hatching can be difficult on a banana peel because the surface texture changes as you mark on it. This makes it harder to keep the lines even.

Smooth Shading: Creates a continuous gradient of color without any discernible lines. The best way to apply smooth shading is to bruise the skin with a blunt tool. You can vary the darkness of the shading by varying the amount of pressure that you apply. This can be difficult to control until you have had some practice. The riper the banana is, the more easily it will bruise and the more quickly the color will darken.

Step 7: Finished Banana

Continue to apply lines and shading until you are satisfied with the level of detail. All the markings will continue to darken over time. The finer details may last a few hours. The overall shape may remain for up to a day. It is a very temporary form of art, so take a picture of it. It's a fun little project to try out the next time that you find yourself stuck in the house on a rainy day.

Step 8: More Banana Art

For more examples of banana oxidation art, check out the work of Phil Hansen and Jun Gil Park.

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