Papir, izdelan med leti 1850 in 1990, ima pogosto pH vrednost v kislem območju. Kisline, prisotne v papirju, pospešijo razgradnjo celuloze in s tem papirja, kar vodi do hitrega slabšanja mehanskih lastnosti papirja. Papir postaja vse bolj krhek in neuporaben, saj rokovanje z njim povzroča dodatne poškodbe gradiva. Iz Narodne in univerzitetne knjižnice (NUK) od leta 2013, z namenom podaljšanja življenjske dobe, pošiljajo večje količine knjižničnega gradiva v postopek masovnega razkislinjenja. V podjetju Hoogduin Preservation B.V. na Nizozemskem knjige obdelajo s postopkom Bookkeeper, pri katerem liste knjig izpostavijo suspenziji magnezijevega oksida v organskem topilu. Cilj postopka je zvišanje pH vrednosti papirja oziroma nevtralizacija kislin in vnos alkalne zaloge, ki podaljša obstojnost papirja. V diplomskem delu sem ovrednotila učinkovitost masovnega razkislinjenja izbrane pošiljke knjig iz NUK. Za ta namen bi bilo potrebno izvesti destruktivne meritve vsebnosti alkalne zaloge, kar na arhivskih izvodih publikacij ni sprejemljivo. Zato v knjige pred postopkom razkislinjenja vstavljajo testne papirje, na katerih lahko izvedemo meritve, ne da bi poškodovali gradivo. Meritve pH vrednosti na površini papirja sem lahko opravila neposredno na arhivskih izvodih monografskih publikacij. Na knjigah, izdelanih med leti 1949 in 1984, sem preverila, ali so primerne za razkislinjenje oziroma ali ima papir v knjigah pH vrednost v kislem območju. Meritve vsebnosti alkalne zaloge pa sem opravila na papirjih iz knjig, namenjenih za odpis, iz obdobja med leti 1887 in 1969, ter na dveh različnih vrstah testnih papirjev, ki so bili vstavljeni v knjige. Izmerila sem tudi pH vrednosti papirjev v raztopini pred in po razkislinjenju. Vsebnosti alkalne zaloge v papirju iz knjig sem primerjala z vsebnostmi v dveh različnih vrstah testnih papirjev – Whatman in Schut – ter ovrednotila njuno uporabnost. Ugotovila sem, da zgolj po izgledu oziroma barvi papirja ne moremo določati, ali je primeren za razkislinjenje, saj je imel tudi bel in čvrst papir pH vrednost v kislem območju. Primerjava pH vrednosti papirja pred in po razkislinjenju je pokazala, da je bilo razkislinjenje uspešno, saj je imelo po razkislinjenju 87 % knjig pH vrednost v nevtralnem ali alkalnem (pH ≥ 7). V povprečju se je pH vseh knjig dvignil za 2,5 ± 0,2 enote. Dve knjigi sta imeli pH vrednosti po razkislinjenju med pH 6 in 7, kar je še vedno sprejemljivo, saj je hitrost kislinske hidrolize pri teh vrednostih že zelo nizka. Vsebnosti alkalnih zalog realnih papirjev iz knjig in testnih papirjev sem primerjala z zahtevami NUK in standarda ISO:18344:2016. Pri obeh vrstah testnih papirjev so vsebnosti alkalnih zalog ustrezale obema zahtevama. Vsebnosti alkalnih zalog v realnih papirjih pa so bile nižje od vsebnosti v testnih papirjih, in sicer 7 od 16 papirjev ni dosegalo zahtev NUK, medtem ko le 4 papirji niso ustrezali zahtevam iz standarda. Vsebnosti alkalnih zalog v Whatmanovih testnih papirjih so bile primerljive z realnimi v primerih, ko so bile primerljive tudi začetne pH vrednosti, in sicer nad 5 in pod 7. Pri realnih papirjih, ki so imeli začetni pH pod 5, so vsebnosti alkalnih zalog nižje od Whatmanovih testnih papirjev, kar je razumljivo, saj se je del alkalije porabil med nevtralizacijo papirja. Pri vseh testnih papirjih znamke Schut pa so bile vsebnosti alkalnih zalog bistveno višje od realnih papirjev. Razlog za to je lahko neenakomerna oz. hrapava površina testnih papirjev. Na podlagi vseh rezultatov sem ugotovila, da je za ovrednotenje masovnega razkislinjenja bolj primeren testni papir znamke Whatman. Paper, produced between 1850 and 1990, usually has an acidic pH value. Acids, present in paper, accelerate the decomposition of cellulose and thus the paper, leading to rapid deterioration of mechanical properties of the paper. The paper becomes increasingly brittle and unusable as handling it causes additional damage to the material. Since 2013, in order to extend the lifespan, National and University Library (NUL) has been sending large quantities of library material for mass deacidification processes. At Hoogduin Preservation B.V. in the Netherlands, books are treated by the Bookkeeper process, in which the paper of the books is exposed to magnesium oxide suspension in an organic solvent. The aim of the process is to increase the pH value of the paper or to neutralize the acids and to provide an alkaline reserve, which prolongs the durability of paper. In my diploma work, I evaluated the effectiveness of mass deacidification of a selected consignment of books from NUL. For this purpose, destructive measurements of the alkaline reserve content would have to be carried out, which is not acceptable, therefore test papers are inserted into the books. Measurements are then performed on test papers without damaging the material. The surface pH measurements were performed on archival copies of monographic publications. On books, issued between 1949 and 1984, I checked whether they were suitable for the deacidification process or whether the paper in the books had a pH value in the acidic range. Measurements of alkaline reserve content were performed on books intended for destructive testing, from the period between 1887 and 1969, and on two different types of test papers that were inserted into the books. The pH values of papers before and after deacidification were measured. I compared the alkaline reserves contents in the paper from the books with the contents in two different types of test papers – Whatman and Schut – and evaluated their usability. I found that the appearance or colour of the paper alone could not determine whether it was suitable for deacidification, as white paper with good mechanical properties also had pH value in the acidic range. Comparison of the pH values of paper before and after deacidification showed that deacidification process was successful, as 87 % of the books had pH values in the neutral or alkaline region (pH ≥ 7) after deacidification. On average, the pH of all books increased by 2,5 ± 0,2 units. Two books had pH values after deacidification between 6 and 7, which is still acceptable, as the rate of acid hydrolysis is already very low. The contents of alkaline reserves of real papers from books and test papers were compared with the requirements of NUL and the ISO: 18344:2016 standard. In both test papers, the contents of alkaline reserves met both requirements. The contents of alkaline reserves in real papers were lower than the contents in test papers, namely 7 out of 16 papers did not meet the requirements of NUL, while only 4 papers did not meet the requirements of the standard. The contents of alkaline reserves in Whatman test papers were comparable to the real paper from books, which also had comparable initial pH values, above 5 and below 7. In real papers, which had initial pH values below 5, contained lower amounts of alkaline reserves in comparison to Whatman test papers, as part of the alkali was consumed in the process of neutralisation. In all Schut test papers, however, the alkaline reserve contents were significantly higher than those in real papers. The reason for this may be uneven or rough surface of test papers. Based on all the results, Whatman test paper was found to be more suitable for evaluation of mass deacidification.