How to Colour Glass Ornaments With Sharpies

I originally saw this trick used in making tie dyed t-shirts with Sharpies and rubbing alcohol. I'm not really into tie dye shirts so I tried it out on a different medium, glass; specifically, I wanted to use this technique to paint a glass ornament for Christmas.  In this instructable I will show you how I did just that.

This instructable if my contribution to the Instructable Advent Calendar 2011

While making my ornament it occurred to me that this project demonstrates some simple principles of solution chemistry so I included a learning objective and a discussion of the science behind it so I can enter it into the Teacher Contest.

Step 1: What You Will Need:

• Clear glass ornament -you can get these at craft stores (or any other glass object you want to decorate)
• Sharpies or other permanent markers
• Rubbing alcohol (use in a well ventilated area and away from open flame)
• A dropper/pipette and a small spray bottle
• Newspaper or drop cloth to protect your work surface
• (Optional) disposable gloves

Step 2: The Science

Learning objective:  By decorating a glass ornament with sharpies students will observe the properties of solutions, solubility, the precipitation of solids when a solution becomes supersaturated and at the same time they will be creating art.

Permanent markers are designed to be waterproof, which means that the ink (solute) does not dissolve in water. However it does dissolve in alcohol. The solubility of the solute in a solvent is generally due to polarity. If the polarity of the solute and solvent is the same then it will likely be soluble, so in this case the ink has the same polarity as alcohol but not water (compare image 3 and 6 above).  

When you drop or spray alcohol on ink drawn onto the glass surface the ink dissolves into the alcohol forming a solution (see image 3 above).  The solution spreads out over the surface of the glass (see image 4).  As the alcohol evaporates the concentration of solute increases and the ink begins to precipitate depositing the ink onto the glass creating interesting patterns of colour  (see image 5 above).

Step 3: Making the Ornament

• Cover your work surface with old newspapers or a drop cloth. 
• Wipe your ornament clean first with rubbing alcohol to remove fingerprints and other debris.
• Either hang your ornament or prop it on something (I used a deep lid from a bottle) so that it doesn't roll around. 
• Start by drawing a few small circles of colour and dropping or spraying some rubbing alcohol on it.
• Once the alcohol evaporates add more colour and alcohol filling in the empty spaces on the ornament until you are satisfied with the results.

Tips

• The more rubbing alcohol you add the more the colour spreads, however the colour will also becomes more diffuse.  Experiment with the volume so you know how much you need to create the effect that you want.  Because of the round surface of the ornament, if you add to much alcohol the colour will run down the sides and drip off the bottom.
• I found that you have more control when you use the dropper. Also the spray bottle can cause splattering.
• Be careful with the choice of colours you put together.  If you blend complementary colours you end up with an ugly brown/black colour.
• If your are not happy with the final result, just soak a paper towel with rubbing alcohol and wipe it clean to start again.