6d mark 2

For visual evaluation of the toughness of cured adhesive, the adhesives were uniformly coated on 1.1 mm glass slides (Beijing Lanyi Chemical Co., Ltd.) with a rate of 200 g/m², and then placed in an oven at a temperature of 130 ± 2 °C for 2 h. After adhesive curing, the coated glass slides were placed in a desiccator for 30 min. The cooled glass slides were photographed using a Digital Single Lens Reflex (Canon 6D Mark II).

Baleen whale earplugs were weighed and measured before storing in a −30 °C until processing. After removal from the freezer, all whole earplugs were bisected using medical grade zirconia ceramic scalpel blades or ceramic knives. A frozen bisected earplug was polished using progressively finer grain sandpaper (80–600 grit), rinsed using deionized water and photographed using a Canon DSLR camera with macro lens (Canon 6D Mark II). The SLR camera was mounted to a copy stand with adjustable fluorescent lighting (Bencher Copymate). Digital photographs were taken and used to age the whale by counting the number of dark and light laminae, assuming the combination of one dark and one light lamina (growth layers) constitutes one year of life^{23 (link)}. Before delamination, two independent readers used digital photographs to age each earplug included in this study. One additional reader was used if there was greater than a ± 5% discrepancy in the total laminae counts.