(3) In accordance with Article XXXIII (4) The Contractor shall cause to be of the contract, all materials, supplies and articles incorporated in the permanent structures shall be of the highest grade, free from defects and imperfections, of recent manufacture, and unused (unless used articles are furnished by the Government). Workmanship shall be of the highest grade and in accordance with the best modern standard practice, furnished guarantees against any failure, in proper use or operation, caused by omissions of material, defective material, workmanship or deSign, for a period of one year from the date of final acceptance of the completed work, all machinery and equipment, parts and assemblies thereof (except equipment and for machinery furnished by the Government ) for which guarantees are customarily furnished in the trade, or for machinery and equipment of special design, for which detail designs or requirements are not prescribed in the specifications. f. Preference for Domestic Articles - Because the materials Tisted below or the materfals from which they are manufactured, are not mined, produced, or manufactured, as the case may be, in the United States in sufficient and reasonable available commercial quantities and of a satisfactory quality, their use in the work herein specified (subject to the requirements of the specifications) is authorized without regard to the country of origin: Asbestos Chromium Clay, English ball Clay, English china Copper, natural - nickel alloy Cork Jute Kaurigum Lac Nickel O11, chinawood (tung o11) Platinum Rubber Silk Sisal Tin Wood, Balsa Wood, Teak Articles, materials, or supplies manufactured in the United States and containing mercury, antimony, tungsten, or mica of foreign origin may be used (subject to the re- quirements of the specifications) in the work herein speci- fied because such manufactured articles, materials, or supplies, have been manufactured in the United States subStantially all from articles, or supplies mined, produced, or manufactured, as the case may be, in the United States. GC-9