Scavo

Archaeology has always been a cornerstone for my art, and I love my work to have that "just-unearthed" look. I also adore the look of vessels dredged up from thousand-year-old wrecks in the Aegean covered with the hoary crust of time. So, how to apply the dust of centuries? Decorazione a Scavo is a traditional Italian technique that does just that. It's usually referred to for short as "scavo," which literally means an excavation or archeological dig - hence "excavation decoration."

There are many formulas for creating scavo effects. They range from applying leaded encrustations to hot glass, which is then soaked after it cools in water and scrubbed to remove most of it, to simply encasing the hot object with fine ground white sand. The result is an object that looks like it is from an old collection perhaps slightly devitrified or, with heavier application, something that has been pulled up out of the sea.

I also have a little bit of the mad chemist in me and I love to mix and melt! I started playing with scavo years ago, and I want to share my formula and variations. The chemicals are easy to come by, the application method is easy, and the results are delightful.

Skill level - beginner

What you need:

Soft Italian glass-making supplies
Potassium nitrate
Calcium carbonate
Mortar and pestle
Small glass custard bowls
Compatible enamels
Reduction frits
Colored glass frit
Teaspoons
Liquid soap
toothbrush

First, a word about the chemicals. Potassium nitrate is sold as tree stump remover at any nursery or discount megastore and is very easy to come by. The kind I use is sold by the pound in plastic bottles. Potassium nitrate is a caustic chemical, so please follow all label precautions, and always work with proper ventilation! For occasional use, the gasses are negligible, but if you intend on working with it a lot please wear a respirator.

Calcium carbonate is also called "whiting," but don't buy the kind sold in the hardware store, as it is made by grinding limestone, chalk, or marble. You need the extremely purified version sold in ceramic shops which is produced by precipitation.

Step 1

Open the stump remover. It should look like small beads and has to be ground up. Put 2 teaspoons into the mortar. Grind in a circular motion until all the beads are broken down. This takes about 10 seconds. Some of the mix will still look a little coarse, but that's good, since it will add to the artistic effect.

Step 2

Place 1 teaspoon of the ground potassium nitrate into a custard cup, then add 2 teaspoons of whiting. Mix thoroughly. That's my base scavo mix.

Step 3

Scavo is really at its best on large beads. It can be a little messy, so make sure whatever is under your torch can be easily cleaned. Make a bead. When you have put all the finishing touches on it, it's time to add the scavo. Take the bead out of the flame and sprinkle the base scavo mixture over it. It will hiss and sizzle. Sprinkle in clumps. Return to the flame and make sure it is burned in. Usually 3 or 4 seconds in the flame will do it. You can then add more and keep burning in until you get the effect you want - anything from just a little aging to craters of the moon! It's easy to see what is happening to the bead as you are working. Once you are happy with it, put it into the kiln to anneal.

Step 4

Coloring the base mix is easy. That's where the fun begins, and you can put your own imprint and style onto it. Use whatever enamels you regularly use on your glass beads. I have made a chart of my enamels by fusing them onto a sheet of white glass. It's so much easier to see what the colors will really look like that way. About ¼ teaspoon of enamel to 1 teaspoon of mix will give you nice colors. The other fun things to add are reduction frits and colored glass frit. In the photo I have added several different frits and a pinch of enamel to the base mixture in the dish.

Step 5

Make another bead. When you have put the finishing touches on the bead start adding the colored scavo just here and there until it looks like it's time-worn and encrusted. If you have used reduction frit, now is the time to turn down the oxygen and reduce it in the propane flame. I have made two different colored beads with the same frit/enamel mixture to show you the different looks you can get. Put your beads into the kiln to anneal.

Step 6. Once the beads are cool, use a soft toothbrush and some liquid soap to gently scrub the bead to remove any loose scavo. If you have burned it in correctly this should be a very small amount, if any, but often where it does come off you are left with what looks like an oil slick on the bead, which is very attractive. Make sure you write down what additions you made to the base mix that you especially like. Otherwise, if you are like me, you'll forget the next day! I keep my leftovers in baby food jars with the formula written on them. Store any unused mixtures in a cool dry place. I hope my scavo mix will appeal to the mad scientist in you. Enjoy!