Origini dell'ucronia. La letteratura contro la storia

L’ucronia (Alternate History) è un fenomeno letterario ormai popolare e molto studiato, ma non lo sono altrettanto lo sue origini e i suoi rapporti con la storia “fatta con i se” (Counterfactual History), che risale a Erodoto e a Tito Livio. Solo nell’Ottocento alcuni autori, per vie largamente autonome, fecero della storia alternativa un genere di fiction: Louis Geoffroy con Napoléon apocryphe (1836), storia «della conquista del mondo e della monarchia universale», e Charles Renouvier con Uchronie. L’utopie dans l’histoire (1876), storia «della civiltà europea quale avrebbe potuto essere» se il cristianesimo fosse stato fermato nel II secolo. Questi testi intrattengono relazioni complesse con la letteratura dell’epoca di genere sia realistico, sia fantastico, ma altresì con fenomeni di altra natura: la storiografia, nelle sue forme e nel suo statuto epistemico, e ancor più il senso del possibile - o la filosofia della storia - derivato dall’esperienza della rivoluzione e dal confronto con le teorie utopistiche e di riforma sociale. Altri testi, prodotti in Inghilterra e negli Stati Uniti nello stesso periodo, esplorano le possibilità narrative e speculative del genere: tra questi P.s’ Correspondence di Nathaniel Hawthorne (1845), The Battle of Dorking di George Chesney (1871) e Hands Off di Edward Hale (1881); fino a una raccolta del 1931, If It Had Happened Otherwise, che anticipò molte forme e temi delle ucronie successive. Queste opere sono esaminate sia nel contesto storico e letterario in cui furono prodotte, sia con gli strumenti dell’analisi testuale. Una particolare attenzione è dedicata alle strategie di lettura prescritte dai testi, che subordinano i significati al confronto mentale tra gli eventi narrati e la serie dei fatti autentici. Le teorie sui counterfactuals prodotte in altri campi disciplinari, come la storia e la psicologia, arricchiscono la comprensione dei testi e dei loro rapporti con fenomeni extra-letterari.

The effect of linseed oil on the properties of lime-based restoration mortars

The traditional lime mortar is composed of hydrated lime, sand and water. Besides these constituents it may also contain additives aiming to modify fresh mortar´s properties and/or to improve hardened mortar´s strength and durability. Already in the first civilizations various additives were used to enhance mortar´s quality, among the organic additives, linseed oil was one of the most common. From literature we know that it was used already in Roman period to reduce water permeability of a mortar, but the mechanism and the technology, e.g. effects of different dosages, are not clearly explained. There are only few works studying the effect of oil experimentally. Knowing the function of oil in historical mortars is important for designing a new compatible repair mortar. Moreover, linseed oil addition could increase the sometimes insufficient durability of lime-based mortars used for reparation and it could be a natural alternative to synthetic additives. In the present study, the effect of linseed oil on the properties of six various lime-based mortars has been studied. Mortars´ compositions have been selected with respect to composition of historical mortars, but also mortars used in a modern restoration practise have been tested. Oil was added in two different concentrations – 1% and 3% by the weight of binder. The addition of 1% of linseed oil has proved to have positive effect on mortars´ properties. It improves mechanical characteristics and limits water absorption into mortar without affecting significantly the total open porosity or decreasing the degree of carbonation. On the other hand, the 3% addition of linseed oil is making mortar to be almost hydrophobic, but it markedly decreases mortars´ strength. However, all types of tested lime-based mortars with the oil addition showed significantly decreased water and salt solution absorption by capillary rise. Addition of oil into mortars is also decreasing the proportion of pores which are easily accessible to water. Furthermore, mortars with linseed oil showed significantly improved resistance to salt crystallization and freeze-thaw cycles. On the base of the obtained results, the addition of 1% of linseed oil can be taken into consideration in the design of mortars meant to repair or replace historic mortars.