Patented Nov. 15, 1949 ’ 2,488,507 UNITED j STATES PATENT OFFICE , SYNTHETIC STAR RUBIES AND STAR SAP PHIRES, AND PROCESS FOR‘ PRODUCING SAME John N. Burdick and John w. Glenn, Jr., Ken more, N. Y., assignors to The Linde Air Prod ucts Company, a corporation of Ohio No Drawing. Application August 27, 1947, Serial No. 770,942 19 Claims. (01. 63-82) 1 This invention relates to a process for develop Other-objects are to provide a process for ing asterism in natural and synthetic corundum developing asterism in single crystals of ruby. crystals, such as crystals of ruby and sapphire, and sapphire containing oxide of titanium; to which contain oxide of titanium dissolved in provide a process for obtaining star ruby and alumina. The invention is also concerned with .star sapphire gemstones from non-asteriated asteriated single crystals of synthetic corundum single crystals of ruby and sapphire containing as articles of manufacture, for example synthetic oxide of titanium; and to provide a process for star rubies and star sapphires. intensifying asterism inasteriated ruby and sap For more than thirty years massive nongran phire crystals. ular synthetic rubies and sapphires of gem qual 10 The term “massive non-granular,” as used ity have been produced commercially on a large herein, is intended to designate singlev crystals scale by the process of Verneuil, as disclosed in as distinguished from‘ a sintered or agglomerated U. S. Patents 988,230 and 1,004,505. In that proc mass of granules. Moreover, this term is further } ess powdered alumina, with or without small intended to designate crystals which are larger percentages of coloring oxides, drops through 15 than such tiny particles or granules of corundum an oxy-h'ydrogen ?ame, fuses, and accumulates as are commonly employed in abrasives, those on a refractory support until a long, narrow, crystals designated by the term “massive non approximately cylindrical boule of the desired granular” being, indeed, large enough to be used size is formed. Boules weighing several hundred in jewelry settings and of a size su?icient that carats are common. For rubies the color may 20 any asteriation present in them can be readily be imparted by chromium oxide. In blue apprehended and appreciated with the naked eye. sapphires, small'quantities of titania and iron ' The term “of gem quality.” as used herein, is oxide are often used. Sapphires of othercolors intended to mean that the crystal is su?lciently can be produced by including with the alumina ‘perfect to warrant cutting, polishing, and oifer small quantities of one or more. other oxides, 25 ing for sale as an ornament._ such as those of manganese, cobalt, vanadium, We have found that asterism can be developed and nickel. v ‘ arti?cially in a massive nongranular single crystal There are occasionally found in nature as of ruby or sapphire of gem quality which contains teriated rubies and sapphires which, when cut en oxide of titanium dissolved in alumina. This is cabochon, i. e. with a convex surfaceopposite 30 accomplished by heating such a crystal at a tem a substantially‘ plane surface, exhibit a, well perature within the range between 1100° C. and de?ned six-rayed star when observed under re 1500’ 0., and maintaining the crystal constantly ?ected light, particularly from a point source. ata temperature within that range until a com--v Such crystals, usually called star rubies or star pound of titanium (probably titanium dioxide) sapphires, are highly prized, and there is a great precipitates along prominent crystallographic demand for them. Also prized are ‘rubies andv planes of the crystal. The length of the heating sapphires having such a structure and cut in period required‘ varies as an inverse function of such a manner as to show but one ray. ' the temperature, being less at the higher tem Although the Verneuil process for manufactur peratures than at the lower temperatures. The ing synthetic corundum crystals, and the result 40' best heating time for any selected temperature ing product, have been subjected to intensive re is readily determinable by trial. As examples search for many years, asteriated rubies and, of suitable heating schedules, asterism was suc sapphires were never produced synthetically prior cessfully produced in both synthetic ruby and to the present invention. In fact, according to synthetic blue sapphire boules after 72 hours at Kraus and Slawson, in' their book “Gems and 4.5 1100° C., after 24 hours at 1300° C., and after 2 Gem Materials,” (1941) “As it has notkbeen pos hours at 1500° C. Below 1100° C. no asterism de sib'le to produce'synthetic rubies or sapphires. veloped. Above 1500'’ C. no precipitation of th which show asterism, star rubies and star sap-I oxide of titanium occurred. ‘ phires must have been cut‘ from the mineral.” vFor best results, the alumina powder from The principal object of the present invention v whichthe crystals are grown should contain at is to provide asteriated single crystals of syn least 0.1% and not more than 0.3% of T102. thetic corundum, such as synthetic ruby and Above 0.3% TiO2, considerable di?iculty is en sapphire of various colors. Another object is ' countered in growing the boule. to provide cut synthetic star rubies and star sap Among the. ruby and sapphire crystals suc phires. ' cessfully asteriated by the above—described pro- ‘ 4 cedure were a white sapphire half-boule grown varying as an inverse function of the temperature. from a powder containing 99.9% of Also: and 3. A process for developing asterism in massive 0.1% of TiO:; a blue sapphire half-boule grown nongranular single crystals of ruby and sapphire from powder containing 99.4% of AlaOs, 0.1% of containing oxide of titanium in solution, com T101, and 0.5% of moi; and two ruby half prising percipitating oxide of titanium in such a boules grown from powder containing 2.0% of " ‘crystal by maintaining such a crystal at a tem CraOa,’ 0.1% and 0.2%, respectively, of ‘110:, bal-' perature constantly between 1100° C. and 1500° C. ance AhOa. for between 2 and 72 hours, the length of the Synthetic corundum whole boules treated by heating period varying as an inverse function of wrnovelprocessarecharacterisedbyhavinga. 10 the temperature. generally cylindrical peripheral surface, and a 4. A process for developing asterism in massive cloudy, opalescent skin which contains a heavy nongranular single crystals of ruby and sapphire concentration of the precipitate of titanium com containing oxide of titanium in solution, compris pound, probably titanium oxide. The inner por ing maintaining such a crystal at a temperature tion of the boule is substantially free from pre 16 of about 1300°.C. until oxide of titanium precipi cipitated' titanium oxide. Of course, when a tates in said crystal. whole boule is split along its longitudinal axis in 5. A process for developing asterism in massive a conventional manner to form two half-boules, nongranular single crystals of ruby and sapphire each segment has such a skin only on its cylindri grown synthetically by Verneuil's procedure from cal surface, and is substantially free from precipi an alumina powder containing as an essential in tated titanium oxide throughout the rest of its gredient 0.1% to 0.3% of T102, said process com mass. prising heating such a crystal at a temperature After heat-treating the crystal as described within the range between 1100° C. and 1500‘ C., above. a gemstone is cut en cabochon in such a and maintaining said crystal at a temperature way that the base of the gemstone is normal to the within said range until titanium oxide precipi C-axis with the C-axis extending symmetrically tates out of solution. follow through the center of the stone andthrough 6. A process for preparing star rubies and star the center of its convex crown. The skin may sapphires from non-asteriated massive non be on either the base or the crown. A well-de granular single crystals of ruby and sapphire fined six-rayed star centered in the crown of the containing oxide of titanium in solution, said stone is obtained by this manner of cutting. ‘If process comprising heating such a crystal at a desired, the asteriated gemstone can be cut so temperature within the range between 1100° C. that less than six rays show, as by cutting the and 1500° C.; maintaining said crystal at a tem stone with the C-axis at an angle to, rather than perature within said range until titanium oxide coincident with, the normal to the plane of the precipitates in said crystal; and thereafter cut base of the stone. - ting a gemstone from said crystal en cabochon After cutting an asteriated ruby or sapphire en in such a way that the base plane of said gem cabochon it is frequently desirable to heat or re stone is normal to the C~axis of said crystal. heat it in the range from 1100° C. to 1500" C. to 7. A process as claimed in claim 6, also com intensify the visibility of the star. 40 prising reheating said cut gemstone and main The synthetic asteriated crystals, both out and taining the temperature thereof within the range uncut, contain curved growth lines and micro between 1100° C. and 1500“ C. to intensify aster scopic or submicroscopic oriented acicular crys ism therein. tals which are probably rutile (TiOz) . The visible 8. An asteriated massive nongranular single precipitate is distributed primarily in the surface crystal of synthetic corundum of gem quality con layer or skin of the stone. Natural sapphires and taining a precipitate of a compound of titanium.