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unregistered user
14-Dec-01, 02:53 PM (PST)
"The Strappo Technique"
   The "Strappo" technique explained here is ideal for frescoes on small bricks,support boards, or studio walls. I have used this method to successfully remove works off of large panels, but I would recommend practicing on throw-away pieces first and small. Professional restorers do use some of these principals when removing historical pieces and transferring them to new a support surface. It is a very complicated process and involves numerous tools and materials of a higher quality not mentioned here. Please do not think this information is a "How To Formula" for removing frescoes of historical value and especially ones of a large size. Removing a fresco which has been painted to the exact diminisions of an entire wall is much more difficult than removing one from a frame or studio wall where you can easily get at all of the edges.It takes teams of skilled professionals and much planning! This method may also remove the sinopia painted on the "Arriccio" or paint which has seeped through to the "Intonicco."Just use the same process as for removing the "Velo." There is a wonderful museum in Pisa which displays the wonderful sinopia found underneath the surfaces or early frescoes.


Plywood or fiberglass
(don't use partical board or cheap wood)
"Vernice Gomma Lacca" (cow bone glue-"Cola Di Bue")shellac varnish.Dry Form.
Water (distilled preferable)
Double Boiler (large lobster pot and a smaller pot)
2" Thin Packing Tape (kind that rips easily.light tan)
"Colla Freddo" (cold glue) boat or marine glue...("Caseina")
2" to 3" House Painting Brush(ample bristles,soft)
Paper Towels
2 Large Plastic Mixing Bowl
Cotton Gauze Cloth (#1 Bolt and #2 Bolt)(Like Linen)
Sifter (one which has a canvas bottom to strain liquid materials)
One Dull, Thin Spackling Knife (kind painters use to patch holes or glaze window sills)
Thick Clear Piece Of Plastic (a little bit larger than the fresco)
Sharp Razor Blade

Directions For Strappo:

* Clear a large table to work on. Make sure the work area is clean and free of dust. Prepare as many
things in advance as possible. Be prepared!!!!!

* First select a board that will be used as the support for your fresco. It should be flat and not warped. The size may be slightly larger than the
fresco or the exact dimensions. If you make it a little bit larger, it will mean that the support board and canvas will extend beyond the diminsions of the
fresco. If you use a board to the exact dimension or a hair smaller, any excess canvas and possibly pigment will be trimmed off using a sharp razor blade.

* Cut two identical pieces of cotton gauze which exceed the diminsions on all sides of the fresco by about four to five inches. Do not make it too small!
The cotton gauze used is a #1 and #2. The gauze which has larger openings is used for the "Strappo" and the finer gauze is glued down to the panel support. When finished,one should have two identical pieces of gauze.
One piece from the #1 material and one piece from the #2 material.

* "Colla Di Bue" comes in a dry form. First it must be soaked in water for one hour in a large, plastic mixing bowl. After soaking, strain the mixture
into a second plastic mixing bowl. Use a sifter which has a canvas bottom. The glue may be soaked in a small amount of water. After one hour stir and mix the solution. It should be the consistency of watery syrup (thin and liquidy).Do not know a given ratio...most glue packets come with directions in Italian.Always start on the lesser side and add water until the consistency is achieved. Next remove the mixture and pore it into the double boiler.A large pot is filled with water. Then a second pot is fastened in a way which allows the bottom to rest halfway in the water.The smaller pot will hold the glue as it comes to a boil.

* Brush on the "Colla Di Bue" over the surface of the fresco. Make sure all areas are covered with an ample amount of glue. Place the gauze over the fresco. Stretch it out and try to pull out any wrinkles or bubbled areas (pull on opposite sides of the fabric to do this). Next reapply ample amounts of "Cola Di Bue" on top of the gauze. Make sure there are no dry areas left.Essentially the gauze has glue attaching it to the fresco and glue on top to completely seal it. This provides strength to lift every little piece of pigment or calce. Let it dry in a humid climate for 7 days or in a dry climate for one day.

Transferring The fresco:

* Once the fresco is dry, (use both hands and even pressure) slowly pull the gauze material back. Do not pull hard or at an extreme angel. Be gentle!!!!
After the fresco is off, tape the removed fresco down on a work table. Make sure the canvas side faces down. Take a flat,dull putty knife and slowly scrape off any sand or calce. Be sure to keep the blade at a low angel. Moving it in very small circles prevents pulling up any section of pigment. Work tough spots slowly and from all angels. Tips On Taping.....Lay the
fresco canvas-side down. Carefully place the support board on top of the fresco. Move it until you have the pigment completely covered by the board (like cropping a photo or framing an image). Use this as a guide to tape around the perimeter of the board.Continue with the tape until you reach the outer edges of the canvas.The last pieces of tape should cover 1 inch of your canvas and 1 inch of work table.Now clean the sand and calce off of the fresco (this is literally the backside of the pigment). When finished cleaning, I carefully pull up the fresco and canvas(leave tape attached) and place tape on the reverse side exactly in the same places. This way there is no tackiness to the tape and chance of it sticking to something, during the gluing process.

* Take a second piece of "Fine" cotton gauze and cut it to the same diminsions. Using the support board as a measure again, place sections of tape around the perimeter of the support board...like a frame. Cover the same areas with tape on the reverse side.

* Mix the "Colla Freddo." The mixture is two parts water to one part "Colla Freddo." First fill a plastic mixing bowl with the measured amount of distilled water. Add the "Colla Freddo" and mix with a wisk. Add a bit of lime to the mixture. Once completely dissolved, let the glue stand for Ten Minutes exactly!!! Occasionally stir it...especially if clumps rise to the top of the mixture. It should be the consistency of buttermilk or eggnog. After the ten minutes is up, strain the glue using a canvas based sifter(the canvas on this type of sifter is as thin as nylon pantyhose). This glue is only good for one day!!!!

* (Two people work best and most efficient) Paint the glue on the cleaned pigment-side of the fresco(this is literally the reverse side of the pigment). Get all areas painted with a generous amount of glue. Let this sit for ten minutes, while it gets tacky. Near the five minute mark, paint the board surface with the glue and place over the support board the previously prepared fine cotton gauze canvas. Since this gauze has already been taped, one should be able to line it up within the perimeters of the tape. Immediately paint the top surface of this fine, cotton gauze with the glue in every possible area inside of the taped perimeter (painting top side of gauze.. board is underneath gauze...board,glue,gauze,glue). It is important to stretch out all wrinkles or folds. Do this quickly and with four sets of hands. Remember this is a strong glue and will hold immediately. When I lay this canvas down on the board, I have an assistant hold two corners and myself the others. We then lay it down like we're making a bed. It is important to move quickly and get the wrinkles out. At the ten minute mark, take all four corners of the fresco and place the glued-side down on top of the tacky cotton gauze (the piece which is glued to the board support). Pull any wrinkles out and stretch the fresco to meet the edges of the board evenly. Make sure you frame it on the board quickly and exact because the glue will set up and it is hard to move it more than a few centimeters. Quickly place the plastic on top of the fresco and use the flat part of your hand to smooth out any bubbles. Make sure you push
bubbles to the edge. Make sure to start in the center and work your way out. Do not leave any little area untouched...even if it looks like it is stretched out perfectly. Stretching the fresco tight and getting the air out is essential to achieve a good transfer!!!!!

* Leave the plastic on top of the fresco. Place a board the same size on top of the fresco. On top of this place a heavy weight. It is good to use
something which will displace weight evenly...like a nice wide terra-cotta brick. Sand bags are used on larger works. Let this sit for two hours and
then remove the weight.

* Allow the fresco to dry for one week. Be sure to lay the fresco flat and somewhere it will not be moved.

Completing The Transfer:

* Set up a work area where a good source of hot tap water exists and a good size sink. Have an old house painting brush available (2 1/2" to 3") (make sure bristles are soft and not gunked up), a medium size bowl for hot water, paper towels, and an old white towel (sometimes it is nice to have a dry
towel handy to set the base of the fresco down on)

* Remember too much water will cause glue under the fresco to separate from the board and fresco. Do everything in moderation and focused attention.

* Hold the fresco upright over a sink, bathtub, or shower. Do Not let the fresco rest in the bottom of the sink or area where water collects. This will
cause an area to get water-logged. Take a brush and dip it into a bowl of hot water. Apply amounts of water completely across the top of the fresco (side
to side). Start about one inch below the edge. Work the moisture near the top.Reapply hot water with the brush and work it in circles. You will begin to feel the canvas loosen. Have an assistant try to pick up an edge which is loose and peeled back. Do no force
it up. The canvas will begin to fall on its own. The assistant should hold the canvas and help guide it down. Now that the canvas is moving, keep the
hot water applied to the edge which is just below the loosed canvas...always working across.. side to side. Keep the brush moving in circles and bringing
water as needed. Eventually the whole canvas will slide off. Once the canvas is off, Use a softer brush (4" water color brush) to work isolated spots on
the fresco surface which still have glue immulsion. Gently work directly on the fresco surface; work spots all over the fresco and do not work just one spot at a
time. This will cause a worn mark. Remember the glue dissolves and if you wait and reapply water, the glue will eventually dissolve. After all of the trouble spots are gone, take the entire fresco and give it a rinse in luke warm water. Do this quickly and do not overdo it!!!!!

* note... If you have a small water heater or a low temperature for hot water (a big problem in Italy), a person may want to consider keeping water
at a boil on the stove. Periodically remove a pot full to have ready to replace a luke warm pot of water.

* After the canvas has been removed, allow the fresco to dry upright. Do not leave it in direct sunlight or in an environment where the heat is strong.

Touch Ups and Wax:

* Some areas of the fresco pigment may not have transferred successfully or there may be areas where the artist wishes to add additional information to
the existing pigment. Retouch the fresco using the yoke of an egg and a dash of vinegar (just a little bit). Mix the colors with the yoke and some distilled water if necessary. The colors will dry as they appear when mixed. Let the paints dry for 1/2 an hour to one hour.

* If the fresco is dry, one may apply wax to the surface of the fresco. Use a soft cotton rag when doing this and apply it gently. Be sure to spread it out completely and make sure to get it in all areas. One coat may do or possibly two light coats...depends on how dry the surface is.I personally wait two days before waxing the surface, if I have done in-painting.

* Let the wax-coated fresco dry for at least two hours and then buff it gently with a clean, soft cotton rag.

* Last, trim the excess canvas off carefully. Take the cut right to the very edge of the panel.

* If any of the edges are slightly peeled up, use the "Colla Freddo" to glue down these areas. Cover with plastic and place a small amount of weight on
this surface for a few hours. Be careful not to put too much weight because the fresco pigment is not protected any more and there is only plastic over
it. Textured surfaces transfer and you may snap off a nice raised up section
of pigment.

Building A frame:

* I design my frames before I begin painting the fresco. All of the construction,sanding,staining, or painting is completed ahead of schedule. Once I am ready to place the stretched fresco in its new home, I only have to carefully assemble to pieces around the work. It is not wise to take the chance of dripping or dropping a tool on the surface of your fresco. IT IS VERY DELICATE!!!!. My frames never allow anything to rest on the fresco. The frame pieces rest flush up against the work. A snug fit and anchoring devices from behind work best. I like to have no visible screws or hardware visible.

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  Subject     Author     Message Date     ID  
  RE: The Strappo Technique sian 28-Feb-02 1
     RE: The Strappo Technique Mozart 01-Mar-02 2
         RE: The Strappo Technique Mozart 03-Mar-02 3
             RE: The Strappo Technique sian 04-Mar-02 4
             RE: The Strappo Technique Iliamoderator 05-Mar-02 5
                 RE: The Strappo Technique Mozart 07-Mar-02 6

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unregistered user
28-Feb-02, 03:27 AM (PST)
1. "RE: The Strappo Technique"
In response to message #0
   Hi! I would be most grateful if anyone could answer some questions that have been bothering me, particularly regarding the strappo technique. Regarding large frescoes and sinopias in museums such as the ones in Pisa you mentioned and the ones in Mantua by Pisanello, how have they managed to separate the sinopia layer from the fresco layer which has been painted on top? Is it using the technique you describe?
Also, when you sketch a sinopia how do you actually use it, if you are going to plaster over it when doing the fresco? How is it possible to see the original sinopia design when you are painting, if there is a fresh plaster layer on top of it?
And finally, I recently saw some frescoes in a church covered in "scars" where bits of the plaster had been very deliberately hacked off. Not all the frescoes in the church were damaged like that, but I wondered what the reason behind it was. SOmebody said that they covered the church in lime when it was used as a hospital and needed to hack through the fresco so the lime wash would adhere to the wall, but this didn't explain why all the frescoes were not damaged in such a way.
Thanks a million for any advice!

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unregistered user
01-Mar-02, 07:55 AM (PST)
2. "RE: The Strappo Technique"
In response to message #1
   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.


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unregistered user
03-Mar-02, 12:48 PM (PST)
3. "RE: The Strappo Technique"
In response to message #2
   Dear Sian,

Here is a follow up on your question about how artists were able to paint once the sinopia was covered with plaster.......

It is important to know when a fresco was painted. Frescoes you will find in the sinopia museum in Pisa are from the early 1300'. Frescoes which date before the mid 1400's had to deal with the issue of limited access to large sheets of paper. It was expensive and depending on the amount of money provided for a project determined whether an artist could afford it
or whether they chose to incur this expense.

Large sheets of paper inable an artist to enlarge drawings to scale to use as a refernce when working and also they are able to make transfers,or spolvero, which allows an artist to transfer an image directly onto the velo. Artists would also glue these large sheets together to make even bigger sheets of paper.
Michelangelo wrote of garzoni glueing sheets of paper together to prepare for his fresco "The Battle Of Cascina." It is recorded that he had the entire mural drawn and maped out for this mural. Pretty big!!!

For the artist working in the earlier times, they would first paint the entire mural on the arriccio using a reddish paint made from a clay which comes from syria. The preliminary painting was named after the paint...."Sinopia." Artists would carefully lay plaster to fit an exact portion of the painting.All work painted on the velo at this point is from memory and from using drawings as reference to the information underneath. Because artists were not bound by strict transfers, one sees a departure from the sinopia and with that which was actually painted. Some areas are faithful to what was planned in the sinopia. Other areas depart completely..sometimes omitting figures or adding figures.

Studying sinopias has shed light that artists before the Renaissance had a better understanding of perspective and the rendering of forms three diminsionally. Many of the early sinpoias are as interesting as the actaul frescoes and are also works of art in themselves.

Hope this has helped.



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Member since 4-Mar-02
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04-Mar-02, 04:55 AM (PST)
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4. "RE: The Strappo Technique"
In response to message #3
   Dear Mozart

This has been fascinating reading and I am very grateful indeed. Thanks so much!


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05-Mar-02, 12:31 PM (PST)
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5. "RE: The Strappo Technique"
In response to message #3
I have to add that for a large fresco sinopia is essential as a composition reference, as the painter has to work in sections attaching/lining up giornatas. Without to scale reference it would be quite a difficult if not impossible task.

Just imagine that you are to paint a complicated composition on 36" by 48" canvas, but the task is to paint it in 10"X10" odd shaped segments starting from a blank canvas. You are allowed to sketch and paint only one little segment at the time and go to the next one only after the previous is completely rendered in color. You are also not allowed to paint over previously painted segments.



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unregistered user
07-Mar-02, 11:12 AM (PST)
6. "RE: The Strappo Technique"
In response to message #5
   Dear Ilia,

Good Point. A veteran like yourself knows it is an artform which is 90% planning and 10% execution. Once you are on the project site,you already spent a considerable amount of time with the composition and reworking it to be prepared for the big day of painting. I imagine it was no different back in the dark ages!!!

take Care Mozart

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