Painting on Location
by Donald A. Jusko

Fresco Painting
Intonaco Mortar Time Test

Bird of Paradise, 3-5-4, First Fresco Painting

03-01-04, Board intonaco test 1.
On a dry brown coat that was scrubbed to remove any carbonate that had formed on the top and was rewet with lime water until it wouldn't take any water from the intonaco layer, I did four tests. From left to right in 1:1 proportions, crushed limestone and slaked lime, crushed limestone and small sand, small sand only, medium sand only.
2:25 PM, Finished applying intonaco. 3:25 still too wet to paint on, it's a rainy day.
Now some timed pigment absorption tests after the intonaco starts setting. Start 4:25 stop 4:50, all have color on them. absorbed well, will give coats at:
6:00 = top left viridian, the mortar is still very wet.
7:00 = top right viridian, still soft mortar.
8:00 = lower left viridian
9:00 = lower right viridian, I think the best absorption is now, the mortar is firmer.
10:00 = left center viridian, it doesn't seem like it's pulling.
11:00 = right center viridian, I think it's over, the mortar is still soft enough to push in a dent.

The small limestone first section looked the best while I was painting. None of the sections have any cracks but I would like to try a little higher percent of aggregate, maybe 1.25 to make the intonaco a little dryer as it is still soft at 5:00. I should have put the blob of lime putty on a paper towel to absorb all the outside clinging water. The quantity of lime for this test was so small that the little extra water meant something to the total consistency. The smallest grit is the hardest right now. Making the mortar harder will shorten the absorption time but make the painting a lot easier.

Day 2, It's still raining out this morning and the mortar is not real hard, tomorrow should be the real test time. No cracks! Scrubbing the lower mortar layer did it, that plus soaking it in limewater.

Day 6, all the viridian colored dots are locked in, no cracks.

fresco color test


6:30 PM, Intonaco made with finely sifted limestone and lime made as dry as possible and blotted on paper towels, 1:1, troweled on a scrubbed rough coat with large sand and lime 1:1.

Side 1 has rabbit skin glue added to the mortar, side 2 is plain.
8:20 PM, This test will tell which side absorbs pigment the longest. Waiting for the shine to leave and it become firm enough to touch. A stripe will be added using pigment and limewater, each 15 minutes starting at 8:30, the color is caput mortum.
9:30 PM, both still going good. Changing to smaller strokes or I'm going to run out of space. 10:00 feels very good on both sides, the mortar is still soft but I can touch it without making a mark. 11:00 still feels great on both sides, the mortar is firm. 12:00 both sides still absorbing great. I'm really pleased with the smooth white surface in the sifted limestone section.
1:30 AM and both sides just won't give up, great absorption, I'm getting tired, maybe I can take a nap and wake up in an hour, 2:48 all is well, I woke up at 5:11 and it was closed.

9:00 AM, a few hairline cracks. I don't know what that's all about, the same mortar in the 03-01-04 test of different aggregates is doing fine. I'm not positive yet, but maybe 2:00 was the end. I thought 2:00 applied well, maybe it was just so close to the end all the pigment didn't sink in far enough and left some on the top. I'll know for sure tomorrow. the only difference was the rough coat was a little thicker.

I've learned the intonaco can't be more any more then 1/8th inch thick.

3-6-4, 2:00 AM was the last test stroke that locked in on both sides. Five and a half hours painting time. More time then with sand in the intonaco.

fresco time test


Board Z2, intonaco on 2:00
Acrylic bonder on rough coat.
Acrylic bonder in intonaco side 1.
Rabbit skin glue in intonaco side 2, really dries mortar, I had to add a little more lime and lime water.

3:00, Painting. It's slow to absorb at the start while the mortar is soft, soft enough for the softest brush to make a mark. It takes about 5 minutes for the sprayed color and shine to dissipate. As the absorption time decreases the mortar gets harder. I'm using an air brush for the background, it takes many passes. I think it would have been faster with a big brush loaded and used during the later faster absorption period. That was a first thought.. More spraying as time went on made a very nice background.

4:20, I was painting the "Bird of Paradise". Our neighbor down the street has a whole clump growing. No drawing, just painting the flower with sure strokes. By 5:50 blending was fun and I could see light at the end of the tunnel. I know I have another 2 hours of absorption time and I'm just floating along. I can't tell the difference between the rabbit glue side and the adhesive/binder side, it's written on the back but there is no need to look. I hope neither side cracks. I'll know in 2 days. Neither side cracked but neither additive is needed.

6:15, Finished, Pigment colors: Titanium White, naples Yellow, Viridian Extra warm side, Cadmium Orange, Cobalt Blue Light, Quinacridone Red, Thalo Blue.

Color drawing progression

Buon Fresco

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