Achaeometrical Research in Hungary II., 1988

PROSPECTING and DATING - János CSAPÓ - Zsuzsanna CSAPÓ-KISS - János CSAPÓ JR.: How the amino acids and amino acid racemization can be used and with what limits for age determination of fossil materials in archaeometry

presence of either tyrosine or methionine. The methionine content of the samples decreased to 85% of the original level in 100-140 years, to 55% in 400-500 years and to almost nil in 1600-1700 years. Tyrosine decreased 10-15% in 100-140 years, 30% in 400500 years, and was almost completely decomposed at 1600-1700 years. Regressions of age on amino acid content were based on analyses of the 23 samples having known ages (Table 14) which were described in Tables 10 and 11. The amino acid contents of the modern carpet were not included in the estimation of regression due to curvilinearity introduced by including that sample. These curvilinear functions resulted in large differences between known age (y) and predicted age (y) at the extreme ages. Since we cannot extrapolate regressions beyond the range of the data, equations developed in this study can be expected to apply to wool samples 120 to 1700 years of age. Linear regression equations, correlations and standard errors of estimate (s

y x

) for the regressions of age on amino acid contents are shown in Table 15. Based on the correlations and errors of estimate, cysteic acid content was the most accurate estimator followed by tyrosine and cystine contents. The cysteic acid/cystine ratio was a less accurate predictor than either of the components of the ratio and methionine content was clearly the least accurate predictor. Table 15 Equations, correlations (r

xv

) and errors of estimate (s

v x

) for linear regressions of age on amino acid contents of wool carpets and wool threads of copt textiles of different ages Independent Variable Equation (a + bx) r

xy s

y.x Cysteic acid(xj) ĵ =-335 + 467* .996 55.3 Cystine (X2) y =2068-453x

2 -.981 124.9 Tyrosine (X3) y =1770-599x

3 -.988 100.4 Methionine (X4) y =1539-3601x

4 -.855 334.5 Cysteic acid/cystine (X5) y =366 + 401x

5 .974 146.1 Correlations among the various amino acid contents were extremely high. Considering the three most accurate estimators, correlations were -0.980 for cysteic acid and cystine, -.990 for cysteic acid and tyrosine, and +0.970 for cystine and tyrosine. As a results of these high correlations between independent variables, very little could be gained by using multiple regression. However, the average of estimates based on cysteic acid, cystine and tyrosine was found to have a standard error of approximately the same size as that based on cysteic acid alone. Use of the average of estimates allows compensation for errors of analysis for individual amino acids. 43