When a student of fine arts or a ceramist approaches the archive for the first time, the questions tend to follow a pattern. They are not about abstract theory. They are about what can be done with the materials, how long the process takes, and whether the results are reproducible outside a laboratory.

One of the most frequent questions is about the origin of the ashes. Not all wood produces the same flux. The archive holds records of tests with ash from holm oak, Aleppo pine, and kermes oak, each yielding a different melting point and a distinct hue in the final glaze. The question is not trivial: choosing the wrong wood can ruin a batch of vessels that took weeks to shape.

Another recurring concern is the temperature curve. Students ask whether a simple pit firing can reach the 850 °C needed to vitrify the ash-iron mixture. The answer is yes, but the atmosphere must be controlled. A reduction atmosphere turns the reds into greys; an oxidising one preserves the ochre and brick tones. The archive includes diagrams of firing pits used in the Iberian period, with notes on fuel layering and oxygen intake.

The third question is about durability. A decorative piece does not need to hold grain, but a storage vessel does. The clay body must be dense enough to resist cracking after repeated thermal cycles. The records from the Ebro valley show that adding fine sand and chamotte to the ferruginous clay reduces shrinkage and improves thermal shock resistance. Students often ask for the exact proportions, and the archive provides them, along with the caveat that local clays vary.

Finally, there is the question of colour. How do you get a deep red without modern pigments? The answer lies in the hematite content of the clay and the ash composition. The archive contains a table of colour results from different combinations of clay sources and wood types, measured under controlled firing conditions. It is not a recipe book, but a reference for those who want to experiment with informed choices.

Publicado el 15 de marzo de 2025 · Categoría: Arqueometría