Is it safe to irradiate historic silk textile against fungi?

The finding of heavily damaged historic silks prompted this study to answer the title question on possible unwanted effects of fungal decontamination by gamma-irradiation. Although silk fiber constitutes of relatively stable protein fibroin heritage silk textiles need protection from biodegradation. Low-dose (0.5−2 kGy) gamma-irradiation is already recognized as a fast, temperature independent method of insect eradication. For fungal decontamination, somewhat higher absorbed doses are needed. Since possible unwanted side effects to already damaged material must be excluded, model samples were prepared by aging contemporary silk. Some of the unaged and aged samples were irradiated to 6 kGy and other to a much higher dose of 120 kGy to identify radiation-specific damage, if any. In order to achieve detectable damage selected irradiated and non-irradiated model samples were subjected to further artificial aging. None of the assessment methods used (ATR-FTIR, SEM thermal analysis) revealed any radiation-specific change. Provided that the fibroin conformations are identified and analyzed separately, FTIR is the method of choice for monitoring the effects caused by any treatment of silk. An increase in the amide I/II absorption intensity ratio is a sensitive though ambiguous indicator of silk degradation. Transformation of more stable beta-sheet to alpha/random coil fibroin conformation is a definite proof of degradation. It occurred exclusively on artificial aging of model silks and was accompanied by pronounced morphology changes confirming the role of conformation on silk stability. In non-treated historic silks the fraction of more stable beta-sheet conformation was unexpectedly high as was the iron content that likely protected silk structure. Since irradiation produced insignificant and likely partially reversible effects radiation treatment of silk textile is deemed safe beyond the absorbed dose proposed as an upper limit for fungal decontamination, 8 ± 2 kGy.