I am always looking for ideas for my Chem Club and I came across a craft article on how to etch a metal tea kettle1 using salt water. I had an extra box of roofing tins and decided to give it a try. I was able to etch Christmas designs into these metal circles. It worked beautifully. [These roofing tins are most likely galvanized steel.]
The materials are easy to get and inexpensive. You can find a variety of holiday hole punches to use at Hobby Lobby or Michaels — plus they have weekly 40% off coupons. A 5-lb box with 750 disks was about US$10 and purchased at Home Depot. The students loved their creations and the etching. It was easy to set up and clean up.
The process etches out some of the surface metal. The exposed metal is oxidized and metal ions form. These positively charged ions are removed by rubbing with a negatively charged salt solution on a Q-tip — the ions in the salt solution conduct the electricity. As always, try a sample to see what type of metal would work best. This method is used to etch stencils into stainless steel cutting knives.
- Tin roofing caps. These tins were already cut in circular disks. They are used to hold down the paper or felt under the shingles. Holes were made in advance with a hammer and a nail.
- Contact paper — an inexpensive material with a decorative surface on one side and adhesive material on the other side.
- Q-tips dipped in a salt solution
- Two electrical leads with alligator clips. I purchased mine from American Science and Surplus (great website for supplies)
- 9-volt battery
- Cover the roofing tin with a stencil made with Christmas hole punch in contact paper.
- Attach the roofing tin to the positive electrode of the battery using one set of alligator clips. Make sure that the alligator clip is touching bare metal.
- Thoroughly wet one end of a Q-tip with salt water solution or vinegar and salt solution. Use the other set of alligator clips to attach the wet part of the Q-tip to the negative electrode of the battery.
- Using the alligator clip as a handle, press the wet end of the Q-tip against the metal of the design. Then slowly and evenly go over the whole design. It should take about two minutes. Replace the Q-tip when it gets dirty.
- Rinse the design and dry. Remove the stencil and attach a ribbon through the hole. It is ready to hang on the tree.
Happy crafting with chemistry.
Safety and disposal
Gloves and goggles should be used. Check local regulations about disposal. There is very little product on Q-tips. The MSDS for each of the potential products should looked up. For example, one should be look up tin(II) acetate.
[In Canada, we were not able to find these roofing tins. We tried large flat washers — stainless steel (CDN $1.39 each) and galvanized steel (CDN $0.49 each). You can see the results of the stainless steel washer on page 16, top photo. As with any activity, we recommend teachers try this beforehand — especially because each metal may have a varying result. For example, on the galvanized steel washer, the Q-tip did not turn black. We also had little success with zinc washers.
It should also be noted we used one 9V battery for only two ornaments before it no longer seemed to work. We did not verify the battery was dead. Most of the cost of this activity will likely be batteries. One would want to source inexpensive batteries for this activity.]