## 2 Materials and Methods
### Sample Selection  
A total of 48 film and photographic reels made of cellulose acetate were selected for testing. Three further reels, made of different materials (i.e., polyester-PET, cellulose nitrate), were added to act as negative controls for the test. For each sample, the degradation level and corresponding acetic acid concentration were determined using A-D strips. The samples chosen are reported in Table 1, along with information provided by the owner, degradation level determined by means of A-D strips, and corresponding acetic acid concentration in the film box [18]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{**Owner/Code**} & \multicolumn{1}{c}{**Film Name**} & \multicolumn{1}{c}{**A-D Strip Level**} & \multicolumn{1}{c}{\begin{tabular}{c} **Acetic Acid** \\ **Concentration (ppm)** \\ \end{tabular} } \\ \hline \multicolumn{4}{c}{**Fondazione Alinari Per La Fotografia**} \\ \hline Alinari sample 0 & 3 photos: Construction site & 2.5 & 18.0–20.0 \\ \hline Alinari sample 1 & Photo of office & 0 & \(\leq\)0.5 \\ \hline Alinari sample 2 & Photo of industrial machinery shop & 0 & \(\leq\)0.5 \\ \hline Alinari sample 3 & Photo of electrical equipment & 0 & \(\leq\)0.5 \\ \hline Alinari sample 4 & Technical specification for equipment & 0.5 & 0.5–1.0 \\ \hline Alinari sample 5 & Various symbols on pentagram & 0.5 & 0.5–1.0 \\ \hline Alinari sample 6 & Photo of office reception & 0.5 & 0.5–1.0 \\ \hline Alinari sample 7 & Photo of art piece & 0.5 & 0.5–1.0 \\ \hline Alinari sample 8 & 3 photos: 1 people dining, 2 and 3 press conference & 0 & \(\leq\)0.5 \\ \hline Alinari sample 9 & Photo of building & 1 & 1.0–2.0 \\ \hline Alinari sample 10 & Photo of Italian street & 1 & 1.0–2.0 \\ \hline Alinari sample 11 & 2 photo reels: column and archeological pieces & 0 & \(\leq\)0.5 \\ \hline Alinari sample 12 & 3 photos: TV show & 0 & \(\leq\)0.5 \\ \hline Alinari-B/W photo films & \
\begin{tabular}{c} 5 photos: 1 inside of office, 2 outside of historical \\ building, 3 inside of restaurant, 4 man adirring \\ paintings, 5 people discussing \\ \end{tabular} & 0.5–1.0 \\ \hline Alinari-B/W photo reel & 3 photos: official meeting & 1 & 1.0–2.0 \\ \hline Alinari-red hue photo films &
\begin{tabular}{c} 3 photos: 1 airplane storage, 2 and 3 photos inside \\ homes at Christmas \\ \end{tabular} & 0.5 & 0.5–1.0 \\ \hline Alinari–color photo film & Photo of Pantheon–Rome & 0.5 & 0.5–1.0 \\ \hline \multicolumn{4}{c}{**Institut Valencia De Cultura (Filmoteca Valenciana)**} \\ \hline
00010820 & Publicidad Rico Famosa & 3 & \(>\)20 \\ \hline
00011242 & Febus Comic 4 Publicidad & 0.5 & 0.5–1.0 \\ \hline
00015797 CulturArts 5 & “Easy street” (Charlot en la calle de la tranquilidad) & 2-2.5 & 8–18 \\ \hline
00015798 Cultur Arts 7 & Canario Roj & 1.5 & 3–5 \\ \hline
00015799 Cultur Arts 6 & Maigret en el caso de la condesa & 0.5 & 0.5–1.0 \\ \hline
006113 & Las Truchas & 0.5 & 0.5–1.0 \\ \hline
**Deustches Filminstitut \& Filmmunseum** & & \\ \hline DFF\_12\_21 & Das Wachsfigurenkabinett & 0 & \(\leq\)0.5 \\ \hline DFF\_12\_556 & Nosferatu & 0 & \(\leq\)0.5 \\ \hline DFF\_12\_584 & Das Lied der Nachtigall & 0 & \(\leq\)0.5 \\ \hline DFF\_3.01.35.01 & Fire & 0 & \(\leq\)0.5 \\ \hline DFF\_3.01.35.03 & Herbstgeschichte & 0 & \(\leq\)0.5 \\ \hline DFF\_3.01.35.04 & La parola Amore esite \({}^{\text{a}}\) & 0 & \(\leq\)0.5 \\ \hline DFF\_3.01.35.16 & Leolo & 0 & \(\leq\)0.5 \\ \hline DFF\_50\_500A & Bergbauer (Kurzfilm) \({}^{\text{a}}\) & 0 & \(\leq\)0.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Real film samples used in this work. For each are reported information provided by the owner, A-D strip level. Films marked with \({}^{\text{a}}\) are made of PET instead of cellulose acetate.