A composition of matter exhibiting a sharp color change upon transition from a liquid state to a solid state or from a solid state to a liquid state, capable of being supercooled for at least several minutes, and substantially free of impurities, to form a solid solution when the composition is in a solid state, consisting essentially of:
- (a) a solvent adapted to change from a solid state at substantially a predetermined temperature to a liquid state;
- and
- (b) an effective amount of an indicator material selected from the group consisting of pinacyanol iodide, thionin, methylene blue, cresol red, neutral red iodide, neutral red chloride, crystal violet, acridin orange, Orasol Orange RLN.TM., Orasol Navy Blue .TM., Irgalith Red PR.TM., Fat Red BS.TM., Xylene Cyanol FF.TM., Rhodamine B.TM., Rhodamine 6G.TM., Irgalith Magenta TCB.TM., Irgalith Pink TYNC.TM., Toluidene Blue O.TM., Savinyl Green B.TM., Savinyl Blue RS.TM., purpurin, 3,3'-diethylthiadicarbocyanine iodide, cryptocyanine, Dicyanine A.TM., Merocyanine 540.TM., 4-(p-ethoxyphenylazo)-m-phenylene diamine hydrochloride, Yellow Orange S.TM., Chrysoidan G.TM., fuchsin, aurintricarboxylic acid (ammonium salt), Victoria Blue R.TM., Pyronin G.TM., gallein, Erythrosin Yellow Blend.TM., chlorophenol blue, bromophenol blue, bromocresol purple, Coriphosphine O.TM., acriflavine, acridine orange, rhoduline violet, Alizarin Cyanine 2R.TM., Alizarin Red S.TM., alcannin, Aurantia, Direct Green G.TM., Fast Salt Red 3GL.TM., Fast Salt Blue BB.TM., Fast Garnet Salt GBC.TM., Carta Yellow G 180 0/0.TM., murexide, Savinyl Blue GLS.TM., Irgalith Blue GLSM.TM., phthalocyanine, Di Amingreen B.TM., Alizarin Blue S.TM., Celliton Blue Extra.TM. , neocyanine, Janus Green.TM., dimethyl yellow, Fast Yellow.TM., methyl red sodium salt, Alizarin Yellow R.TM., Eriochrome Black T.TM., Chromotrope 2R.TM., Ponceau 6R.TM., Brilliant Ponceau G/R/2R.TM., chromolan yellow, Sudan Red B.TM., Bismark brown G.TM., Fat Black.TM., Resorcin Brown.TM., Benzofast Pink 2BL.TM., Oil Red EGN.TM., Euroglaucine, Fuchsin NB.TM., parafuchsin, Patent Blue.TM., Irgalith Blue TNC.TM., Phloxin B.TM., fluorescein sodium salt, Rhodamine B base.TM., Eosin Scarlet, Eosin Yellowish, Erythrosin extra bluish, 4,5-dibromofluorescein, ethyleosin, Phloxin.TM., Cyanovin B.TM., chlorocresol green, pinacyanol bromide, 2-(p-dimethylaminostyryl)-1-ethylpyridinium iodide, ethyl red, nigrosine, Savinyl Blue B.TM., Orasol Blue BLN.TM., Safranin O.TM., Azocarnum G.TM., Phenosafranine.TM., Azocarmine BX.TM., Solophenyl Brilliant Blue BL.TM., Nile Blue A.TM., gallocyanine, gallamine blue, celestine blue, methylene green Azure A/B/C.TM., Blue VIF Organol.TM., Alizarin, Nitrofast Green GSB.TM., quinalizarine, Oil Blue N.TM., Solvay purple, Ciba Blue.TM., Indigo Synthetic.TM., Chromophthal Bordeau RS.TM., Acid Alizarin Red B.TM., 5-amino-fluorescein, Rose Bengal.TM., Martius Yellow.TM., Chicago Blue 6B.TM., Alcian Blue 8GX.TM., cresyl violet, 4,4-bis(dimethylamino)-benzylhydrolzinc phthalocyanine, Sudan III.TM., Pyronin Y.TM., Toluylene Blue.TM., cresyl violet perchlorate, Mendola's Blue.TM., Phosphine Dye, Nitron.TM., cresyl violet acetate, Ceres Orange R.TM., 4-phenylazo-1-naphthyl-amine, 4-(4-dimethylamino-1-naphthylazo)-3-methoxybenzene sulfonic acid, Bindschedler's Green.TM., and p-(p-dimethylaminophenylazo)-benzoic acid dissolved in and inert towards said solvent and adapted to change color of the composition visible to the naked eye upon the change in state at substantially the predetermined temperature when so dissolved.