“Step two in the fresco art-making
Is quicklime’s hydrational slaking.
Lime plaster resulting
For next steps’ constructing:
Adhering-to-wall undertaking.”
The 16 April 2024 limerick continued the pathway of its predecessor, looking at the second step of the three-step fresco cycle, a process called slaking.
“Step two in the fresco art-making /
Is quicklime’s hydrational slaking…”
The reaction summarized here is symbolized as follows, as the quicklime (CaO) formed in Step 1 of the fresco cycle (calcination) is mixed with water, causing an exothermic reaction and the formation of calcium hydroxide: CaO (s) + H2O (l) → Ca(OH)2 (l)
The reaction equation corresponds well to “quicklime’s hydrational slaking,” since quicklime is one reactant and water is the other.
Two quick tangents here: first, “in the limelight,” as an idiom, refers to the intensely bright light caused by the behavior of quicklime, yet another fascinating point that I had never encountered until writing these pieces. While unrelated to fresco, it seemed too good to pass up as a post title, since quicklime is still involved in this step.
Second, “hydrational slaking” is admittedly redundant. However, the latter term seems less familiar to students each time I teach. I am sure I will persist in mentioning “slaking one’s thirst” in class as another way of saying “taking a drink of water,” since it seems a rare one-to-one correlation between everyday meaning and specialized vocabulary.
“Lime plaster resulting /
For next steps’ constructing: /
Adhering-to-wall undertaking.”
The product in this reaction is “calcium hydroxide” to a chemist and “lime plaster” to a fresco artist. It will be used in the next step, of constructing the fresco art itself. A fresco consists of two plaster layers, the arriccio layer, adjacent to the wall, followed by the intonaco layer, the actual painting surface. Both involve calcium hydroxide; the key difference between the two is the coarseness of the sand mixed into the plaster (finer sand is used for intonaco).
Chemphasis 