Dear Sian,

The technique of strappo is ideal in removing the top layer which is known as the "velo" (veil or velotura (spelling) means to paint in thin veils of color). After the Velo is removed, you will see paint has seaped through and there will be large areas of color resembling the surface. It will look like the design but out of focus. This layer may also be removed in the same process. If the fresco is relatively a new work, the first two layers pull away from the arriccio with no problem at all. Remember that before a fresco is painted, the arriccio below has cured and dried completely. It also has a roughed foundation to hold to and sometimes a lattice work of reed or nails driven into the surface. This last layer holds to the wall like a barnacle to a ship's hull.

The technique for removing sinopia is not the same as strappo. I must say that I am not a professional restorer and have not learned this technique for my training as a fresco painter. What I write here is from observation and brief learning on the subject. Hopefully a restorer will post a response. The technique for removing an entire fresco is known as "stacco." It takes a few assistants and equipment to do this job, especially if it is a large work. The process is similar to strappo except that more layers of the fresco are removed. The restorers must use various tools to work the plaster away from the wall. Imagine a large role of paper towels on a dispenser. As the fresco comes off it is roled up onto a large tube which gets larger and larger as the fresco peals off. The restorers carefully scrape and wedge tools between the wall and the fresco. The restorers may remove the entire fresco or just the first two layers. The sinopia is on the arriccio and may now be removed using the strappo technique. All of these works may be mounted on despayed in museums or their original locations.

I have to go an teach a class now, but I will post again to answer your questions about the problem of painting and covering up the sinopia.

Mozart