First Presidency offers instructions on making of endowment.
Joseph F. Smith, Letter to Ward Bishops, December 31, 1912, in Devery Anderson, The Development of LDS Temple Ceremonies (Salt Lake City: Signature Books, 2011), 162
The garments worn by those who receive endowments must be white, and of the approved pattern: they must not be altered or mutilated, and are to be worn as intended down to the wrist and ankles, and around the neck. Please inform all to whom you use recommends that these requirements are imperative, and that admission to the Temple will be refused to those who do not comply therewith. The Saints should know that the pattern of endowment garments was revealed from heaven, and that the blessings promised in connection with wearing them will not be realized if any unauthorized change is made in their form, or in the manner of wearing them.