Xiandai Fanggu Ciqi Ruhe Biancheng "Gudai Zhenpin"
Title in English:
How Replicas of Ancient Porcelain Become "Genuine Ancient Works"
Authors:
(The Relics Protection and Archaeological Science Lab in Shanghai Museum)
Wang Weida Xia Junding
With the development and application of ThermoLuminescence (TL) technology used in determining the dates of ancient porcelain, replica makers already know that modern replicas of ancient porcelain can be changed to "genuine ancient works" by simply applying a certain artificial dosage of c or neutron irradiation to disturb the TL authentication. In order to bring to light this forging method, this article focuses on the related study we did.
We randomly chose 4 replicas of ancient porcelain. Figure 1 is an imitation of a porcelain bowl of the Qing Dynasty numbered 164-1. Figure 2 is an imitation of a blue and white porcelain vase of the Ming Dynasty numbered 143-2. Figure 3 is an imitation of underglazed red vase of the Yuan Dynasty numbered 101-1. Figure 4 is an imitation of ji zun made in jun yao (yao=kiln) of Northern Song. To these four wares we applied artificial irradiation with amounts equivalent for Qing, Ming, Yuan, and Song dynasties as listed in Table 1. Then we used the method as described in the article "Qian Jiliang Jishu he Ciqi Niandai Ceding" (Predose Technology and the Determination of Porcelain Dates) published in the same issue of this journal and also introduced in "Qian Jiliang Baohe Zhishufa Yanjiu"' (Predose Saturation Indexes Research) to determine their dates. The procedures are as follows:
(1) Making Samples.
This involves 2 steps. First is drilling for a sample. A special tube-like drill which measures 50mm in length and 3 mm in inner diameter is used. At 2mm both inside and outside of the drill head is plated with fine emery. It is virtually an emery drill. A cylindrical sample of 3-5mm long and 3mm in diameter is obtained from the thick bottom part of the porcelain. Boron carbonate or water is always used as coolant while drilling for the sample. Next step is slicing the samples. We used the Slicer II model made by the Mlavem Company in England whose slicing speeds are arbitrarily adjustable to slice as thin as 50 µm with a tolerance of <10%. Each cylindrical sample can be sliced into 4-6 pieces of about 200 µm, the thickness most appropriate for irradiation of ß rays in the lab'. A detailed description of the sampling can be found as numbered 3 in the reference materials listed at the end of this article.
(2) Laboratory Work
The automatic irradiator model SIPK manufactured by Amersham Radiative
Chemistry Center in England is used. Radioisotope for ß source Sr-90, intensity 40mCi.
(3) TL Measuring
The full-automatic ThermoLuminescence/Optical Stimulated Luminescence datemeasuring system from Denmark (Model Riso TL/OSL-DA-15) was used. We took a thin sliced sample to which TAC (Thermal Activation Characteristics[?]) curve is done in order to determine the TAC temperature of the sample. (Refer to the article "Qian Jiliang Jishu he Niandai Ceding" for a description of the measuring method.) For the majority of porcelain, the TAC temperature is between 600-700° C. Then we took another sliced sample to do the following:
(a) Heating and annealing while heating speed depends on the features of the sample;
(b) Measuring the sample's original sensitivity So using a fixed experimental dosage;
(c) Heating the sample to its TAC temperature;
(d) Measuring the sample's natural accumulative sensitivity S,, using the same dosage;
(e) Applying to the sample the laboratory (3 dosage and trying TAC again;
(f) Measuring the sample's natural plus (3 dosage sensitivity SO with the same experimental dosage;
(g) Repeat steps (e) and (f) to measure Sn+2 ß.
We made DS1=Sn+ß - Sn. and DS2=Sn+2ß - Sn+ß, did the linear regression to the 2 pairs of data (Sn, DS1) and (Sn+ß, DS2), got the y-intercept a and the slope b of the straight line, then got the ancient dosage of the samples through Formula 9 described in the article "Qian Jiliang Jishu and Ciqi Niandai Ceding" (same issue of the journal). Divide the ancient dosage by annual dosage, you get the real date when the porcelain was made. Table 1 lists the dates determined through the artificial irradiation to the 4 contemporary replicas. The dates without marked "m" in the numbering column of Table 1 are their real TL dates: respectively 23, 15, 10, and 22 years before present. When irradiated with artificial dosages equivalent to Qing, Ming, Yuan, and Northern Song, their TL dates were measured the same as those marked with "m" in the numbering column of Table 1, that is, 260, 523, 647, and 1030 B.P., matching their expected dynasties. It is noticed that the counterfeiting effects are quite in place.
Table 1. How contemporary porcelain becomes "ancient"
Now take 143-2 the replica of Ming blue and white vase for example. Figure 5 shows its predose sensitivity response curves. The four curves of sensitivity intensity in the figure are, from low to high, So, Sn, Sn+ß, and Sn+ß, with their corresponding readings listed at the upper right corner of the figure. Based on these curves, we got the ancient dosage of the sample, which, divided the annual dosage comes the real age of the sampe: 15 years old. After artificial irradiation, the predosage sensitivity response curves measured (numbered 143m-1) are as illustrated in Figure 6. In comparison with Figure 5, the intensity of Sn is significantly increased from Sn=3930 in Figure 5 to Sn =11510 in Figure 6, a result of artifical irradiation. The TL date of this vase is 523 years before present based on the calculation of the 4 curves in Figure 6. The results from artificial irradiation on the other 3 replicas are the same. In this way, contemporary porcelain becomes "ancient." However, TL scholars have since seen through the trick. In order to explore new technology to identify if artificial irradiation has been done, we plan to carry out research in the following two aspects:
(1) Equivalent dosage of artificial irradiation
This is an important basis to identify artificial irradiation. Because the equivalent dosage is unknown or impossible to know for professionals of non-TL technology, they often apply dosages of artificial irradiation much more than the equivalences. We need to do more research on the equivalent dosage so as to identify whether artificial irradiation is applied or not.
(2) Identification through a dose
Since a dose cannot be artificially fabricated, it is possible to determine whether irradiation is applied or not by checking if there is a dose. The natural radioactive elements in ceramic materials, uranium, thorium, and kalium produce three kinds of natural rays, a, b and c. They differ significantly in the range in ceramic wares: a is 20-50 microns, b is 1-3 millionmeters, and c 20-40 centimeters. First work on the fine
grains of 3-8 microns in diameter from the porcelain to measure the ancient dose in the ware. As the grains are so fine, all three rays can penetrate. Therefore, the ancient dose obtained from the fine sample is the total amount of the irradiation dosage that all the natural radioactive materials provide. Then take thick grains of 90-120 microns in diameter or the thinly sliced samples about 0.2 millionmeters thick to measure the ancient dose in the same ware. As the a particle's ray range is very short, a dose has effect only on the surface of the grain or slice. Once the a dose in the surface is etched away using HF, the ancient dose from the thick grain or the slice has only b and c plus cosmical radioactive elements without any a elements. Based on the analysis of the the radioactive elements in a large number of ancient porcelains, it is known that the annual doses of a (referring to the effecive a that is already turned into equivalent b), b, and c plus the cosmical radioactive elements as found in the total annual dose are respectively 45%, 30%, and 25%. This proportion shows that the percentage of the effective a dose is relatively large, almost half of the total. This fact helps. Because in normal circumstances, the ancient dose in the fine grains should be almost one time bigger than in the thick grains or thin slices. If they differ a little or are very close, the porcelain has received no a dose. Therefore the ancient doses are not natural; they are artificially added (since there must be a elements in the natural doses. Artificial a doses cannot reach the inner part because of its short range.) By comparing the two kinds of samples of ancient doses, it can be determined whether artificial a elements have been added to the porcelain. If there is a, it is real; otherwise, it is not. This is a very special method of authentication that no counterfeit can escape. We call it "a dose differentiation method."
With further advance of research, the "artificial irradiation" trick will ultimately be exposed. This is the inexorable law.
Reference materials:
1. Wang Weida, Liang Baoluan, Zhou Zhixin, et al: Nuclear Technology, 1999, 22
(10)
2. Liang Baoluan, Stokes MJ, Xia Junding: Nuclear Technology, 1995, 18 (8): 476
3. Wang Weida, Zhou Zhixin, Xia Junding: Nuclear Technology, 1995, 18 (8): 454