How did they create copies of the artifact based international standard resistance that was followed until the middle of the 20th century?
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$\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$– Community BotCommented Oct 26 at 7:05
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$\begingroup$ I suspect the following might be helpful: Wolff, F. A., Shoemaker, M. P., & Briggs, C. A. (1916). Construction of primary mercurial resistance standards (No. 256). US Department of Commerce, Bureau of Standards. $\endgroup$– Georg EsslCommented Oct 26 at 10:12
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The history, which is followed in its development as published in Metrologia 46 pp 503-511, may be viewed here. The succinct portion of the history is stated in the introductory paragraph to Section 2 regarding Thomas-type resistors. The following is noted -
In the ‘international-reproducible’ system of metrology used from 1893 through 1947 the 1 $\Omega$ value of resistance was defined by the mercury ohm, based on the resistance at 0$^{\small o}$C of a column of mercury of specified physical characteristics. Artefact standards in the form of wire-wound resistors at the 1 $\Omega$ resistance level were developed extensively in this period for comparison with the mercury ohm and as working dc resistance references. The alloy Manganin, with nominal composition 84% Cu, 12% Mn and 4% Ni, was used for a wide range of standard resistors of which many were developed at the German Physikalisch-Technische Reichsanstalt.
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3$\begingroup$ Links can (and do) rot over time, so it is advisable to cite in full to make it easier to find a publication in the future: G. R. Jones, B. J. Pritchard, and R. E. Elmquist, "Characteristics of precision 1Ω standard resistors influencing transport behaviour and the uncertainty of key comparisons." Metrologia, Vol. 46, No. 5, Oct. 2009, pp. 503-511 (DOI 10.1088/0026-1394/46/5/015) $\endgroup$– njuffaCommented Oct 25 at 19:52