One of the training modules I attended in the first year of training as a Restoration Technician was the study and creation of ancient mosaics, thanks to the restorer teacher Alessandra Costa.
The module covered the types of ancient mosaics, the techniques for creating a mosaic and the methods for restoring mosaics.
I created a mosaic starting from the creation on a temporary support on an Eraclit tablet and setting on lime putty, cutting the stone tiles with the appropriate traditional tools of master stonemasons.
I therefore learned how to make a mosaic with the ancient technique, and it was really very interesting.
The technique of mosaic on temporary support
To create this work we based ourselves on the Ravenna technique of the direct method on temporary support, developed by the Ravenna mosaicists led by Roberto Signorini.
With this method the mosaic is made on a temporary support, in our case composed only of lime put on an Eraclit support, on which we have transferred a 1:1 drawing of the tiles using tissue paper and a non-permanent marker.
The mosaic is then covered with layers of gauze glued perfectly, detached from the lime putty support, then cleaned of glue and bedded in the definitive mortar support.
The work phases: analysis of the mosaic subject
First, after receiving the image to be created, we analyzed the color fields and the patterns of the mosaic tiles, to learn how to read it correctly and understand the original execution technique, as well as to distinguish the various materials and colors used, observing both the tiles and the gaps.
We then created an exact copy of the mosaic, complete with all the tiles, on tracing paper, using a fine-tipped permanent marker.
We marked the black tiles with a dot, to distinguish them from the others, also because the black tiles defined the main patterns of the subject’s profile.
We then used tissue paper to reproduce the design backwards, with a non-permanent water-based marker and on the shiny side of the tissue paper, so that we could then “print” it on the lime putty.
Preparing the mosaic tiles
Once we had prepared the design and studied the materials and colors of the original, we prepared the tiles.
The study of the original helped us understand the dimensions of the tiles that we would then have to use, and their rectangular, square shape and triangular for the corners.
The tiles in mosaic artifacts can be glass or stone, mostly in limestone and are chosen for their color and workability.
We had different materials available such as travertine, marble and glass stones, which are supplied in sticks to then be cut with a hammer and chisel.
The hammer is equipped with a widia cutting side for glass tiles and enamels and a steel side for stone tiles.
It’sIt was interesting to learn how to use these tools to try to obtain the desired shapes for the tiles, dosing the force, learning the posture and how to hold the stone to break.
I noticed the different ways in which the different materials are broken, depending on whether they have internal veins, whether they are porous or hard, and the cut also changes depending on the side on which the hammer.
I have therefore learned to appreciate and admire the expert mosaicists who know how to cut the tiles of the desired shape with speed and precision, a job that is not at all easy!
We prepared an abundance of tiles, always observing the shape of the original tiles, and we placed them on small plates, divided by color.
For my work I used the following materials:
- Belgian Black
- Verona Pink
- Grey bardiglio
- White Verona
- White
- Red travertine
- Laguna red
- Green glassy stone M13 S. donÃ
Preparing the temporary support for the mosaic
We then moved on to preparing the support.
The base is an eraclit panel, a material made of wood wool used in construction as a sound absorber, lightweight and suitable for maintaining humidity.
We wet the Eraclit panel well, in order to prepare it to receive the lime putty by slowly releasing the humidity, so as to allow us to keep the lime putty soft for a long time.
Above the Eraclit we spread a layer of lime putty of about 2cm, smoothing it out well, creating a surface as smooth as possible.
The lime putty is the product derived from the cooking of limestone rocks, at about 900 degrees, creating quicklime which is then slaked with water in special tanks, and left to season.
The result is a material with the consistency of cooking cream, used, together with an aggregate or interte (sand, cocciopesto, pozzolana, etc.) to create the mortar.
In our case we used only the putty, without combining it with a binder, in order to create a soft layer in which to lodge the tiles.
Our putty spread on the Eraclit therefore takes on the role of a bedding layer for the tiles.
We spread the putty in two layers, the first by pressing it well on the Eraclit panel with the trowel, making it penetrate the fibres, to make it stick well, the second layer, after about 10 minutes, softer, but flat and homogeneous.
We smoothed out the surface of the putty well, and then let it rest for about half an hour, so that a shiny layer was created on the surface but without too much water, ready to receive the design prepared on the tissue paper.
We carefully reproduced the entire design by making the tissue paper adhere to the putty with the marker drawing, thus printing all the tiles.
The “printing” of the design using tissue paper is enoughdelicate, because if the slaked pencil is too wet the ink expands, making the drawing blurry. If there is too little water, the design will not print well.
You need to press gently with your hand to make the tissue stick, but without dragging too much, otherwise the ink will smudge, making the tiles incomprehensible.
Mosaic composition
After this step, you can proceed to insert the tiles already prepared in the lime, following the drawing shown.
The tiles should be inserted for 1/3 of their height, without pressing too much so as not to make them sink, but trying to obtain a flatness throughout the work.
With patience, you can select the tiles of the right shape from those already cut, following the chromatic fields and the trends of the subject. You can also cut the tiles further, trying to obtain an even more precise shape.
We proceeded with the profile of the bird, following the trends, and then with the fillings, until completing the mosaic as much as possible.
The detachment of the mosaic from the support
After a few weeks we proceeded with the detachment of the mosaic from the temporary support to insert it into the definitive support.
To carry out the detachment, you need to glue a gauze called tarlatan on the surface of the mosaic, wetting it first, with rabbit glue or vinyl glue.
Tarlatan is a linen gauze with a wide, elastic weave, which adapts well to the profile of the tiles to adhere to all of them.
Two layers of tarlatan must be applied, one at a time, one in the direction of the weft and one in the direction of the warp, passing well with the brush soaked in glue over the surface, tapping with the brush so that the glue penetrates into the gaps, gluing the tiles well and letting the glue dry between one layer and the other.
The glue used must be reversible and must not ruin the tiles.
Some of us used bookbinding glue, which is easier to clean from the tiles, I used vinyl glue, which adhered well, but I had a lot more difficulty removing it in the next phase.
Once the glue has dried well, you can detach the mosaic from the support, initially using a trowel to detach it from the Heraclith, removing the parts of dry putty that almost come off by themselves, and then turning it over with the help of wooden panels to clean the tiles from putty and glue even in the gaps, with a brush, tweezers, scalpel and a lot of patience.
The definitive support for the mosaic
We then experimented with different mortar compositions to create the new support for the mosaic.
The thing to keep in mind is that the bedding mortar must be 1:2, with fine-grained sand so as not to disturb the seating of the tiles, which themselves act as an aggregate.
I chose to use a mixture of sand and golden yellow marble in a 1:1 ratio to havere a support with a warm tone, in my opinion suitable for the subject, which even if it will then be covered by the grouting mortar, may be visible in some points.
The setting mortar must be placed on the support following the profile of the design, in our case, with a height of about 2 cm, first spreading a layer over the entire wet Eraclit, pressing to make the mortar stick, and then creating the thickness by shaping it like the subject.
It is good to apply the mortar also on the side of the tiles, so that it penetrates well into the gaps, and keep the setting mortar rough, to make them stick well.
Then proceed to place the mosaic on the bedding mortar, pressing uniformly so as to make the tiles sink almost completely, so that they protrude from the mortar with 1-2 mm, flattening the mosaic well and uniformly.
At this point, after having left it to dry for a couple of days so that the tiles are well fixed on the mortar, you can proceed to remove the tarlatan, wetting the surface with hot water, so as to dissolve the glue, and removing the tarlatan starting from the corners.
Then we proceed to clean all the interstices and tiles from the glue using tweezers, scalpels and wetting to soften it, which with the vinavil was a fairly long operation.
The edge of the bedding mortar that protrudes from the design must then be shaped and lowered, because it will then be covered with the surrounding mortar.
Then we proceed to apply the surrounding mortar, in my case in a 1:2 ratio and composed, in addition to the slaked lime, of cocciopesto for 1/4, black for 1/4 and golden yellow powder for 1/2, of fine but variable grain size.
The effect I wanted to achieve was a warm tone in which the black and cocciopesto dots stood out.
To bring out the aggregates of the surrounding mortar I performed numerous spongings, with the appropriate sponge, which contribute to lowering the putty and bringing out the aggregate parts.
The edges of the mosaic must be checked carefully, so that the surrounding mortar does not cover the tiles, which must stick out uniformly by a few millimetres.
Then the grouting mortar must be prepared, a more liquid filler, in a 1:1 ratio that I chose to compose with 4/5 of golden yellow and 1/5 of cocciopesto, to make it warm and uniform like the surrounding mortar.
The grouting mortar must be placed over the tiles, making it penetrate into the gaps, and then the tiles must be cleaned well by sponging them, as well as the edges of the same.
To complete and finally make the whole pleasant, I chose to paint the edge of the original mosaic with watercolor, directly on the mortar, to give the idea of ​​the original mosaicale.
I really enjoyed the work overall, there are many steps and they allow you to get your hands on different materials, from stones, to glass pastes, to mortar and sands.
I realized the complexity behind the mosaic works and how much skill was needed to make them.
It is absolutely not easy to make the tiles of the desired size, it requires a lot of knowledge of the materials and manual skill, as well as an eye for the combination of colors and for the creation of mortars.
It was interesting to try to obtain different shades of mortar depending on the percentages of aggregate, trying to add sands and pigments, noting how much the cocciopesto colors the mortar, learning that it must absolutely be washed before inserting it into the lime putty.
Unfortunately some cracks are already crossing the surrounding mortar, could it be due to the excessively fine grain size of the aggregates? Is it because the mortar dries too quickly?
The study will continue.
And here is the final result:
