Monday, 22 August 2011

06__New materials and advice: El Paso

I came to El Paso because I found artists here who would help me paint bigger frescoes and experiment.


The Glasbox is making all this possible, because they rent studio space on a month-to-month basis:


Amazing! I found lime putty for sale at American Clay in Albuquerque -- made from a high calcium lime, slaked for about 2 years. Ready-to-use lime putty is all but impossible to find (though try Les Trois Matrons also), but you can not paint fresco without it. Moreover, no one stocks bags of dry quicklime, or even a quality hydrated lime (the lime at Home Depot is not good enough for fresco) -- so it is very difficult to even make the slaked lime putty yourself.

American Clay also sold me angular marble sand, at 30/50 grit and the finer 80 grit; and a small flexible Japanese trowel:

I also bought angular silica sand and other plastering supplies at New Mexico Plaster in Albuquerque:

Bags of silica sand, a roll of nylon mesh, trowels, Weld-Crete, spray bottle, and a tool to "scratch" in parallel grooves:

20 grit (coarser) and 30 grit (finer) silica sands:

I am using Mayacrom (developed at UTEP) and earth pigments on purpose, because they are both safer than colors like the cadiums, and a lot easier to grind than the hydrophobic organic chemical colors, like the phthalos and quinacridones. I also feel that the natural colors would be more round and beautiful.

My first pigment order from Sinopia arrived:

Left to right --


Marble Dust/Calcium Carbonate:
DC8107/ ten kilos

Iron Oxide Medium Mexican Terra Cotta
PCHR1203 /500

Caput Mortuum Reddish Violet

Sinopia, natural iron oxide red
PCP7 /500

Yellow Ochre golden shade warm
PC113NO /500

Raw Sienna deep orange shade
PC21ORS /500

Yellow Ochre Mexico
PC102NO /500

Buckskin brown ocher
DCNO500 /500


Mummy from Armenia
10AGV /50

949601010 /50

Raw Sienna "SAHARA," cool taupe brownish shade
906J4556 /75

Raw Sienna warm shade
PC206RS /50

Extra Pale Yellow Ochre, Limonite Cyprus
190L101 /50

Yellow Ochre, deep tobacco shade from Cyprus
190PM64 /50

Mayan pigment set
799MS /set

--Mayan Indigo Blue

--Mayan Royal Blue

--Mayan Violet

--Mayan Green

--Mayan Yellow

--Mayan Red

Cat, from Focal Point Art in the Glasbox, made some mini mullers by hand, which is very nice for grinding samples of pigments:

Some people use conventional rock tumblers to "grind" pigment in distilled water for fresco. Thus I also bought a MiniSonic MT4SV Vibratory Rock Tumbler from Mama's Minerals in Albuquerque to experiment with (so that I do not have to grind large quantities of pigments by hand):

I also bought a "Cupola Set" from Perkins Jewelers Supply in El Paso, which I will use to crush up colored rocks that I find, using the rubber mallet. I bought the green rocks in Las Cruces, but they originally came from Sonora, Mexico:

(Perhaps we also might be able to crush colored rocks into pigments with the CrazyCrusher.)

I picked up all my other fresco materials in Midland, Texas, and vacated my storage unit:

Drive-in studio -- I unloaded all those heavy materials to my cubby hole in the Glasbox studio:


My frescoes are cracking, and all the experts suggest that the plaster has too much water in it. When the water evaporates too quickly, the plaster shrinks too fast and breaks, leaving "mud cracks" that disturb the dried painted image.

At American Clay they suggested that I use a more precise ratio of lime putty to sand, to avoid excess water. To arrive at that ratio, first one should fill a 500 ml container with sand, and then fill a 1000 ml container with water:

Then he should pour the water into the container of sand -- but only to the top of the sand. The amount of water poured off is the amount of lime putty that should be added to that sand.

For instance, 250 ml of water was poured into 500 ml of 30 grit silica sand. 250ml/500ml = 1/2, water to sand. Therefore it follows that only one part of lime putty should be added to two parts of 30 grit silica sand, to prevent cracking in the plaster mix:

I did the above experiment for the 4 types of sand I bought in Albuquerque, and calculated the ideal lime putty to sand proportions:

20 grit silica sand -- 1 part lime putty, to 2 parts sand

30 grit silica sand -- 1 part lime putty, to 2 parts sand

30/50 grit marble sand -- 1 part lime putty, to 2 parts sand

80 grit marble sand -- (~175ml water, to 500ml sand) about 1 part lime putty to 3 parts sand

These above ratios basically recommend 2 parts sand to one part lime putty, which is the recipe for the browncoat (the 2nd coat) -- and our browncoat in Lubbock successfully dried without cracks earlier this summer, in spite of the drought and heat wave (over 100 degrees every day). Thus the advice is very sound.

However, it is the final coat which we paint on which cracks. That coat, the "intonaco," is made from 1 part lime putty to 1 part fine sand. All the water comes from the lime putty (since I never add water to the plaster), and thus it seems that the lime putty which I am using has too much water (though I always take from the bottom of the bucket, where the solid lime putty has settled). Perhaps the weather is too warm here in the Southwestern United States, and thus the water evaporates too fast from the fresh fresco plaster. Maybe we should be painting fresco in the winter.


The coarser the sand, the thicker the lime plaster can be applied. The first coat is the scratchcoat, and it follows that this is the thickest coat (1/4 inch?). American Clay and other plasterers etched horizontal grooves into their scratch coats, apparently so that the browncoat, the 2nd coat, can hold on better:


American Clay also suggested mixing the 30/50 grit sand with the finer 80 grit sand, as the variety of particle sizes of sand makes for a stronger cement.

Also, they said I might spread a thin set tile mortar over the Hardibacker cement support, to even the surface. The fresco absorbs carbon from both the front and back of the support -- so a uniform support surface will also help the lime dry and carbonize more evenly, which should help prevent cracking.


Daan in Sonora sent me the following informal fresco advice:

1) Substrate should be saturated, but no standing water. Try that first. If the lime plaster takes too long to set, adjust by soaking a bit less.

2) Slaked lime should be the consistency of butter. You should be able to stack a pile 3 times higher than it is wide at the base. Slaked lime settles. Drain off the water. Don't ever add water to the lime sand mix. It isn't necessary. Don't ever use wet sand. These are the most common reasons for cracking.

3) Lots of people are seduced by histories of fine marble dust and impeccably smooth surfaces, but I learned (via Mark Balma via Annigoni) to use a fairly course sand for the intonaco (1-3mm on the longest side). You can plaster a nice smooth surface with this. In comparison, why wouldn't marble dust (at the same 1:1 ratio) suck all the moisture out of the lime??? Lots more surface area.

4) The old 3:1, 2:1, 1:1 sand/lime ratios and 3 layer rule of thumb is a system that works (not very practical on a panel I know). You might be working on a substrate that is too rich in binder without enough aggregate.

5) Follow Cennino Cennini's instructions to the letter and you can't go wrong.

6) The Italian tradition I learned (still alive via Annigoni) insists even a speck of gypsum or cement in the wall is poison. Since prior layers need to be wet or saturated, the moisture will pick up chemicals that cause efflorescence when in contact with active lime, and complicate your fresco chemistry. Diego Rivera used cement in the first layer or two of a 5 layer system. Since his frescoes aren't 100 years old yet, we don't know how well they will last, but whatever works, works. I found 2:1 (sand to lime) on terracotta panels, with a 1:1 intonaco worked pretty well. Even so, getting lime plaster to work properly is all about the suction/absorbency of the wall and previous layers of lime. Once you work on a wall and get the feel of it, it can be done by "feel" with little adjustments in humidity here and there. On a wall, if the wall isn't humid enough, the lime sets before you can get it smooth! If it is too wet, it will be 8:00 PM before the painter can start his days section! So you are forced to get the feel of how lime takes to lime. Changing substrates or working with cement complicates that. I found that even different brands of terracotta (I use terracotta planter bases/dishes) were fired differently. The ones fired at really high temperatures were pretty impervious to water---not absorbent enough to bond with the plaster or create a proper source of moisture/suction. The plaster literally fell off by itself--total failure of adhesion.

7) Always break the lime skin between layers. Just rough it up with a scrub brush.


I need to finish Mrs. Mary P. Merrifield's book on fresco --The Art of Fresco Painting in the Middle Ages and Rennaisance -- where she discusses adding milk and other techniques:


Nicholas Studio is painting fresco at Western Kentucky University, and the students are blogging about the process (which I found out about from a comment in my following blog entry). Not only it is inspiring to read about how other contemporary artists are tackling fresco, but I am learning a lot from their blog.

For instance, when to stop grinding a pigment in distilled water:

"Grind, grind, grind, that pigment! To test to make sure if your done take a little of the pigment on your finger (that is covered in a glove) or on the end of a palette knife and touch it to a cup of distilled water. If it floats then the pigment is ground if it sinks or some of it sinks keep grinding!!"

Also, I learned about making wooden portable panels. And that I can buy pigments already ground in water for painting fresco -- Aqueous Pigment Dispersions -- at Natural Pigments.

It is wonderful how we can consult other fresco techniques and artists worldwide in the 21st century on the Internet. Vasari's artists did not have this advantage.


When I asked Chris, who runs the Glasbox, about welding some fresco frames for me, he became concerned about the strength of the fresco panel. If the rigid panel bends or twists, the fresco will crack and break. So he had a few suggestions about fortifying the undercoats, such as adding polypropylene fibers to the scratch coat instead of using the fiberglass mess (and perhaps to the other undercoats as well). I think the old fresco masters would add human hair to the plaster, to strengthen the undercoats:


Grinding pigments at the Glasbox studio, with a great view of El Paso spread before me:

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