## 1 Introduction  
The primary motivation behind our study was the urgent need for conservation intervention on valuable 16 th-century silk banners stored at the Wavel Royal Castle in Cracow, Poland [1]. We saw this as an opportunity to evaluate the reliability of FTIR-derived estimators and determine if similar trends in estimator values are observed under different thermal aging conditions. Thus, we aimed to ascertain whether artificial and natural aging can be compared using the same FTIR-derived estimators or if more invasive analyses are required to assess the degradation state of the museum objects. The side reason for our work is to investigate whether the accelerated aging experiments can aid in understanding historical samples' natural degradation and behavior. These experiments aim to simulate the effects of natural aging by subjecting the samples to accelerated conditions, including temperature, Volatile Organic Compounds (VOC), and humidity [2]. These controlled stimuli are expected to induce changes that mirror natural degradation reactions. Heritage science, a multidisciplinary field merging science and art, plays a pivotal role here. It enables informed decisions regarding the preservation of artifacts through comprehensive physicochemical analyses of various materials (including _Bombyx mori_ silk). These analyses help determine degradation mechanisms and provide historical information about heritage objects' composition, handling, and manufacturing processes [2]. Understanding the Fourier-transform infrared (FTIR) spectra of deteriorated silk fibroin samples is crucial. FTIR analysis can be conducted without damaging the sample and, in some cases, without extensive sampling procedures (if the object can be placed in the ATR spectrometer attachment) [2; 3]. Analyzing the FTIR spectra of silk samples has been evaluated for a few daces now due to the complexity of the structure of the samples [3]. _Bombyx mori_ silk is a semi-crystalline biopolymer characterized by highly organized nanocrystals enveloped within an amorphous matrix [4]. Fibroin microfibrils, with widths of up to 6.5 \(\times\) 105 nm, are composed of helically packed nanofibrils (ranging from 90 to 170 nm in diameter [2] (see Figure 1)) that consist of heavy and light polypeptides weighing approximately 350 kDa and 25 kDa, respectively [3; 4]. The tertiary structure of the protein is stabilized by various interactions, including van der Waals bonds between peptide segments, hydrogen bonds located around 0.5 nm from the -C=O and N-H groups of adjacent peptides, and disulfide crosslinks [5]. Although various amino acids compose silk fibroin, its crystalline regions consist of patterns composed solely of the simplest amino acids, such as (-Gly-Ala-Gly-Ala-Gly-Ser-Gly-Ala-Ala-Gly-[Ser-Gly-(Ala-Gly)\({}_{2}\)]\({}^{8}\)-Tyr) [5]. Small functional groups, such as methyl or hydroxyl, allow for the close alignment of amino acid chains, facilitating the formation of \(\beta\)-sheet secondary structures in silk's fibroin crystalline regions (see Figure 1). Van de Waals interactions strongly stabilize the packed structure of fibroin \(\beta\)-sheets. The distances between pleats are 3.7 A/5.7 A (the inter-sheet alternating distances), and distances within pleats are 4.4 A (linked with the intra-sheet interchain distance) [5]. Crystalline regions are surrounded by disordered chains enriched with heavier amino acids, known as amorphous regions. The ordered regions contribute to silk's characteristic strength, while the non-ordered regions provide resilience [2]. In heritage science, silk samples undergo natural aging, making it equally important to comprehend the model sample's structure and degradation pathway [2; 3]. Artificial  
Figure 1: Scheme of silk’s fibroin primary and secondary structure. aging is primarily carried out through temperature and light interaction to gain insights into the decomposition mechanism of model samples [3]. This paper specifically focuses on the artificial aging induced by thermal conditions in silk samples.