Quality control of sample material (e.g. charcoal, collagen) is receiving considerable attention in the effort to obtain more reliable 14 C dates. The atomic carbon to nitrogen (C:N) ratio is a useful indicator of contamination and/or degradation of bone collagen. Wool and silk are also composed of proteinaceous material such as bone collagen, and the C:N ratio may also be a useful quality indicator for archaeological wool and silk. Analyses of modern undyed, mordanted, non-mordanted, and naturally dyed silk and wool were done in order to determine a C:N range that indicates the sample quality. The C:N range can be different for every material as the amino acid composition of wool, silk, and bone collagen are distinct. The measured minimum and maximum C:N values were used to set up a C:N range of uncontamined and undegraded wool and silk. Then, the C:N ratio and 14 C were analyzed of archaeological wool and silk samples. The applicability of the C:N ratio as a quality indicator for archaeological silk and wool was shown by the good agreement of the 14 C dates with the presumed historical dates for the uncontaminated samples and the disagreement of the 14 C dates with the presumed historical dates for contaminated samples.