Abstract:
Decorative paints are typically burned in at relatively high temperatures, preferably in connection with the thermal ceramicizing process. In order to provide a glass ceramic panel having a cooking surface with a pleasing deep black, very smooth decoration by a burned-in decorative paint, the glass ceramic panel is formed from a melt that is black and the decorative paint on the black glass ceramic panel consists of a colorless zinc-containing glass flux The colorless zinc-containing glass flux preferably has a composition in wt. %: Li 2 O, 0-5; Na 2 O, 0-5; K 2 O, &lt;2; ΣLi 2 O═Na 2 O═K 2 O, 1-10; MgO, 0-3; CaO, 0-4; SrO, 0-4; BaO, 0-4; ZnO, &gt;0-4; B 2 O 3 , 15-27; Al 2 O 3 , 10-20; SiO 2 , 43-58; TiO 2 , 0-3; ZrO 2 , Sb 2 O 3 , 0-2; and F, 0-3.

Description:
CROSS-REFERENCE 
       [0001]    This is a continuation of U.S. patent application Ser. No. 10/920,944, filed Aug. 18, 2004. The aforesaid U.S. patent application, whose disclosures are incorporated by explicit reference thereto, provides the basis for a claim of priority of invention for the subject matter of the appended claims under 35 U.S.C. 120. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The present invention relates to a glass ceramic panel or cook top having a cooking surface provided with a pleasing black decoration by applying a decorative paint to it. 
         [0004]    2. Description of the Related Art 
         [0005]    Modern cooking ranges have a glass ceramic panel providing a cooking surface, which is partially or also completely coated with decorative paint. These decorative paints are generally divided into the “glazing” or “enamel” category. A “glazing” is generally a glass that is clear or colored in the melt (glass flux), while an “enamel” is a coating material, which contains a colored non-transparent material, such as a pigment, in the glass flux. Colored inorganic compounds can be used as pigments. However the pigments should usually not react or only react slightly with the glass flux. 
         [0006]    The decorative paint is burned in at temperatures, which are below the softening point of the glass ceramic. In this process the respective glass compositions of the glazing or the enamel are melted and form a stable bond with the surface of the glass ceramic. 
         [0007]    The applied decorative paints have different functions. They serve especially for marking cooking zones, for characterizing touch-panels and for decorative design of the cooking surface. The decorative design has the purpose, among others, of protecting the underlying glass ceramic from usage marks (flecks and scratches). 
         [0008]    Particularly popular decorative paints are gray, white and black. The manufacture of a decorative paint, which produces a deep black color on a glass ceramic panel, is very difficult. Instead a dark brown or dark gray color impression is usually produced, when a commercial black pigment and the usual glass flux is used in the decorative paint, because of a chemical reaction between pigment surfaces and glass fluxes during the burning in or baking process. This is caused by the presence of zinc oxide in the glass flux, which shifts the color shade toward brown tones, so that the burned in decorative paint is dark brown or dark gray—but not black. However glass fluxes with a zinc oxide content of up to 4 percent by weight are used in decoration of glass ceramic cooking surfaces, for example GF 1  as described in DE 197 21 737 C1, GF 2  as described in DE 198 34 801 C2 or GF 3  as described in EP 460 863 B1. The reason is that the presence of zinc considerably improves the viscosity behavior during burning in and increases the abrasion resistance of the decorative paint. 
         [0009]    Currently no deep black colors can be produced with zinc-containing glass fluxes in spite of careful selection of black pigments. 
         [0010]    An additional serious disadvantage of commercial “black” decorative paints is that they are substantially rougher than other decorative paints. Thus e.g. the R a  values according to DIN EN ISO 4288 of the currently used “black” decorative paints (“black 1” and “black 2”) are considerably greater than white or gray decorative paints. Since cooking surfaces coated with rough decorative paints very easily collect dirt (e.g. by abrasion of fine metal parts of pans or vessel bottoms) and the rubbed-off particles are especially noticeable, high quality decorative paints for cooking surfaces—especially black decorative paints—should be very smooth (R a ≦0.35μ). 
         [0011]    The color impressions produced during burn-in using conventional “black” decorative paints are listed in Table I. The color value determination was based on the L* a* b* CIELAB color system. The roughness values of these applied known white, gray and black decorative paints are listed in Table I, which appears herein below. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
             
             
               
                   
               
               
                 CONVENTIONAL GRAY AND BROWN ENAMELS 
               
               
                 MADE FROM DIFFERENT BLACK PIGMENTS 
               
               
                 AND THEIR COLOR VALUES 
               
             
          
           
               
                   
                   
                 Glass 
                   
                   
                   
                   
               
               
                 Example 
                 Pigment* 
                 Flux 
                 Color 
                 L* 
                 a* 
                 b* 
               
               
                   
               
               
                 1 
                 Black 
                 GF1 
                 Dark Brown 
                 25 
                 0.2 
                 −0.4 
               
               
                   
                 2700 
               
               
                 2 
                 Black 
                 GF2 
                 Dark Gray 
                 25 
                 0.2 
                 −1.4 
               
               
                   
                 2700 
               
               
                 3 
                 Black 
                 GF3 
                 Gray 
                 28 
                 0.2 
                 −1.8 
               
               
                   
                 2700 
               
               
                 4 
                 Black 
                 GF1 
                 Dark Gray 
                 24 
                 0.2 
                 −0.6 
               
               
                   
                 240137 
               
               
                 5 
                 Black 
                 GF2 
                 Dark Gray 
                 25 
                 0.2 
                 −1.7 
               
               
                   
                 240137 
               
               
                 6 
                 Black 
                 GF3 
                 Gray 
                 28 
                 0.2 
                 −2.0 
               
               
                   
                 240137 
               
               
                 7 
                 Black 
                 GF1 
                 Dark Brown 
                 25 
                 0.2 
                 −0.6 
               
               
                   
                 PS3000 
               
               
                 8 
                 Black 
                 GF2 
                 Dark Gray 
                 25 
                 0.1 
                 −1.6 
               
               
                   
                 PS3000 
               
               
                 9 
                 Black 
                 GF3 
                 Dark Gray 
                 27 
                 0.1 
                 −1.8 
               
               
                   
                 PS3000 
               
               
                   
               
               
                 *The source of Black 2700 is Johnson Matthey, the source of Black 240137 is Degussa and the source of Black PS3000 is Reimbold &amp; Strick. 
               
               
                 L* a* and b* are color value parameters in the CIELAB system. 
               
             
          
         
       
     
         [0012]    The pigment fraction in all examples of decorative paints listed in Table I was 10 percent by weight (i.e. 90% glass flux) and the coating thickness was from 3 to 4μ. The color measurement was performed with a Mercury 2000 spectrophotometer, Series 1165, of Datacolor (light type, D 65 , Observation angle: 10°). The glass flux compositions were taken from DE 197 21 737 C1 (GF 1 ), DE 198 34 801 C2 (GF 2 ) and EP 460 863 B1 (GF 3 ). 
       SUMMARY OF THE INVENTION 
       [0013]    It is an object of the present invention to provide a glass ceramic panel with a cooking surface having a pleasing black decoration provided by a burned-in decorative paint, so that the decoration has a deep black color and a comparatively smoother or less rough surface. 
         [0014]    According to the invention the glass ceramic panel has a melt that is black, the decoration comprises a decorative paint applied to the cooking surface and the decorative paint applied to the black glass ceramic panel contains a colorless glass flux and from 0 to 10 percent by weight of at least one black pigment. 
         [0015]    In preferred embodiments of the invention the glass flux has a glass composition, in percent by weight on the basis of oxide 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Li 2 O 
                 0-5 
               
               
                   
                 Na 2 O 
                 0-5 
               
               
                   
                 K 2 O 
                 &lt;2 
               
               
                   
                 ΣLi 2 O + Na 2 O + K 2 O 
                  1-10 
               
               
                   
                 MgO 
                 0-3 
               
               
                   
                 CaO 
                 0-4 
               
               
                   
                 SrO 
                 0-4 
               
               
                   
                 BaO 
                 0-4 
               
               
                   
                 ZnO 
                 0-4 
               
               
                   
                 B 2 O 3   
                 15-27 
               
               
                   
                 Al 2 O 3   
                 10-20 
               
               
                   
                 SiO 2   
                 43-58 
               
               
                   
                 TiO 2   
                 0-3 
               
               
                   
                 ZrO 2   
                 0-4 
               
               
                   
                 Sb 2 O 3   
                 0-2 
               
               
                   
                 F 
                  0-3. 
               
               
                   
                   
               
             
          
         
       
     
         [0016]    Experiments, which will be described in more detail herein below, have shown that the decoration according to the invention has a very little roughness and a very deep black pleasing impression. 
         [0017]    The above-described preferred glass composition of the glass flux corresponds to that according to the above-mentioned DE 197 21 737 C1 (The subject matter of this DE reference is also contained in U.S. Pat. No. 6,043,171). The allowed pigment fraction is however preferably limited to 3 percent by weight of pure colored pigments. The subject matter of this DE patent document is hereby incorporated herein by explicit reference thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0018]    The objects, features and advantages of the invention will now be illustrated in more detail with the aid of the following description of the preferred embodiments, with reference to the accompanying figures in which: 
           [0019]      FIG. 1  is a perspective diagrammatic view of the topography of a commercial decorative paint, namely White  1 , showing the surface roughness; 
           [0020]      FIG. 2  is a perspective diagrammatic view of the topography of a commercial decorative paint, namely White  2 , showing the surface roughness; 
           [0021]      FIG. 3  is a perspective diagrammatic view of the topography of a commercial decorative paint, namely Gray, showing the surface roughness; 
           [0022]      FIG. 4  is a perspective diagrammatic view of the topography of a commercial decorative paint, namely Black  1 , showing the surface roughness; 
           [0023]      FIG. 5  is a perspective diagrammatic view of the topography of a commercial decorative paint, namely Black  2 , showing the surface roughness; and 
           [0024]      FIG. 6  is a perspective diagrammatic view of the topography of a new decorative paint according to the invention, namely Black (new), which is made from a “coated” or “re-melted” black pigment and glass flux GF 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    Roughness values of exemplary decorative paint coatings of the prior art and of the present invention were measured. Five sections with a sample size of 5.6 mm were measured for each paint coating with an optical method according to DIN EN ISO 4288 (FRT MicroGlider® Unit) and roughness values were calculated with the associated standard deviation from the profile data according to DIN EN ISO 4287. Table II below shows the resulting roughness values of a black decorative paint used in the present invention, Black(new), and various prior art decorative paints and perspective views of the respective surfaces are shown in  FIGS. 1 to 6 , which show their texture or roughness. 
         [0026]    Because of the high glass flux content of the decorative paint the decoration according to the invention has significantly less roughness, i.e. is much smoother, as shown in  FIG. 6 , than commercial black decorations of the prior art shown in  FIGS. 4 and 5 . The smoothness of the decorative paint according to the invention is comparable to that obtained with the white decorative paints, White  1  and White  2  shown in  FIGS. 1 and 2 . The roughness parameters for the example of the black decoration according to the invention as shown in  FIG. 6  are listed under the heading “Black (new)” in the last line of Table II. In contrast the roughness parameters of the examples of the prior art black decorations (Black  1  and Black  2 ) shown in  FIGS. 4 and 5  are listed in lines 4 and 5 of Table II. The example of the black decoration according to the invention shown in  FIG. 6  has good roughness properties, i.e. it fulfills the usual requirements for surface cleaning properties, abrasion resistance, adherence and chemical resistance to acids and bases. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE II 
               
             
             
               
                   
               
               
                 ROUGHNESS VALUES FOR DECORATIVE PAINTS 
               
             
          
           
               
                 Decorative 
                 Roughness, 
                 Roughness, 
                 Roughness, 
                   
               
               
                 Paint 
                 R a [μ] 
                 R z [μ] 
                 R max [μ] 
                 Topography 
               
               
                   
               
               
                 White 1 
                 0.25 ± 0.01 
                 1.72 ± 0.16 
                 1.94 ± 0.13 
                 FIG. 1 
               
               
                 White 2 
                 0.36 ± 0.04 
                 2.66 ± 0.29 
                 4.06 ± 0.83 
                 FIG. 2 
               
               
                 Gray 
                 0.37 ± 0.01 
                 3.24 ± 0.36 
                 4.12 ± 0.59 
                 FIG. 3 
               
               
                 Black 1 
                 0.48 ± 0.03 
                 4.36 ± 0.38 
                 5.15 ± 0.71 
                 FIG. 4 
               
               
                 Black 2 
                 0.44 ± 0.06 
                 4.33 ± 0.58 
                 5.38 ± 0.74 
                 FIG. 5 
               
               
                 Black (new) 
                 0.29 ± 0.05 
                 3.18 ± 0.99 
                 5.59 ± 3.74 
                 FIG. 6 
               
               
                   
               
             
          
         
       
     
         [0027]    Glass ceramic panels are known, which are black in the melt. An especially intense pleasing black decorative effect is obtainable, when the black colored glass ceramic panel comprises a glass ceramic having the following composition, in percent by weight on an oxide basis: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Si 2 O 
                 62-68 
               
               
                   
                 Al 2 O 3   
                 19.5-22.5 
               
               
                   
                 Li 2 O 
                 3.0-4.0 
               
               
                   
                 Na 2 O 
                   0-1.0 
               
               
                   
                 K 2 O 
                   0-1.0 
               
               
                   
                 BaO 
                 1.5-3.5 
               
               
                   
                 CaO 
                   0-1.0 
               
               
                   
                 MgO 
                   0-0.5 
               
               
                   
                 ZnO 
                 0.5-2.5 
               
               
                   
                 TiO 2   
                 1.5-5.0 
               
               
                   
                 ZrO 2   
                   0-3.0 
               
               
                   
                 MnO 2   
                   0-0.40 
               
               
                   
                 Fe 2 O 3   
                   0-0.20 
               
               
                   
                 CoO 
                   0-0.30 
               
               
                   
                 NiO 
                   0-0.30 
               
               
                   
                 V 2 O 5   
                   0-0.80 
               
               
                   
                 Cr 2 O 3   
                   0-0.20 
               
               
                   
                 F 
                   0-0.20 
               
               
                   
                 Sb 2 O 3   
                   0-2.0 
               
               
                   
                 As 2 O 3   
                   0-2.0 
               
               
                   
                 ΣNa 2 O + K 2 O 
                 0.5-1.5 
               
               
                   
                 ΣBaO + CaO 
                 1.5-4.0 
               
               
                   
                 ΣTiO 2  + ZrO 2   
                 3.5-5.5 
               
               
                   
                 ΣSb 2 O 3  + As 2 O 3   
                  0.5-2.5. 
               
               
                   
                   
               
             
          
         
       
     
         [0028]    This black colored glass ceramic, which is marketed under the trademark CERAN HIGHTRANS®, is described in EP 0 220 333 B1. The content of this EP patent application is hereby incorporated here in this disclosure of the present invention by reference. 
         [0029]    Alternatively a suitable decoration effect is obtainable when the black colored glass ceramic panel comprises a glass ceramic, which has the following composition, in percent by weight on an oxide basis: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Li 2 O 
                 2.5-5.5 
               
               
                   
                 Na 2 O 
                   0-3.0 
               
               
                   
                 K 2 O 
                   0-3.0 
               
               
                   
                 Σ Na 2 O + K 2 O 
                   0-4.0 
               
               
                   
                 MgO 
                   0-3.0 
               
               
                   
                 CaO 
                   0-2.5 
               
               
                   
                 SrO 
                   0-2.0 
               
               
                   
                 BaO 
                   0-3.5 
               
               
                   
                 ZnO 
                   0-3.5 
               
               
                   
                 Al 2 O 3   
                 18-27 
               
               
                   
                 SiO 2   
                 52-75 
               
               
                   
                 TiO 2   
                 1.2-5.5 
               
               
                   
                 ZrO 2   
                   0-3.0 
               
               
                   
                 SnO 2   
                 &lt;1.0 
               
               
                   
                 Σ TiO 2  + ZrO 2  + SnO 2   
                 2.0-6.0 
               
               
                   
                 P 2 O 5   
                    0-8.0. 
               
               
                   
                   
               
             
          
         
       
     
         [0030]    The dark coloring is adjusted by addition of 0.02 to 0.6 percent by weight of V 2 O 5  and if necessary by addition of other coloring ingredients, such as Cr—, Mn—, Fe—, Co—, Ni—, Se—, Cl—compounds, in order to assist in establishing the color and adjusting definite color locations. 
         [0031]    This black colored glass ceramic, which is marketed under the trademark CERAN SUPREMA®, is described in WO 02/16279 A1. The content of this latter prior art reference is similarly incorporated in the disclosure by reference. 
         [0032]    The deep black color impression is already obtained according to a first embodiment of the invention with a decorative paint having a glass flux content of 100 percent, e.g. with an unpigmented transparent melting glass flux according to the above-described DE 197 21 737 C1 (GF 1 ). 
         [0033]    The quantitative results of measurements of the color impression of the decorative coatings according to this first embodiment of the decorative paints (GF 1 ), which comprises a 100% glass flux, in comparison to other glass fluxes (GF 2  according to DE 198 34 801 C2 and GF 3 according to EP 0 460 863 B1), which can be used in decorative paints for the glass ceramic cooking surface because of their low thermal expansion coefficient, are given in Table III herein below. According to Table III a clearly noticeable blue-gray color impression is provided by the other glass fluxes GF 2  and GF 3  and they are thus unsuitable for producing a deep black color impression according to these methods. The decorative coating produced with the glass flux GF 1 , on the other hand, is nearly transparent and is somewhat flatter than the glass ceramic, so that the decorative coating on the glass ceramic is observed to be deep black. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE III 
               
             
             
               
                   
               
               
                 COLOR IMPRESSION OF DECORATIVE COATINGS 
               
               
                 THAT ARE 100% GLASS FLUX 
               
             
          
           
               
                   
                 Glass 
                 Color values 
               
             
          
           
               
                   
                 Flux 
                 Color 
                 L* 
                 a* 
                 b* 
               
               
                   
                   
               
             
          
           
               
                   
                 GF1 
                 Black 
                 24 
                 0.0 
                 −0.6 
               
               
                   
                 GF2 
                 Dark blue-gray 
                 25 
                 0.0 
                 −2.7 
               
               
                   
                 GF3 
                 Bright blue-gray 
                 31 
                 −0.3 
                 −4.3 
               
               
                   
                   
               
             
          
         
       
     
         [0034]    The color values or parameters of the decorative paints consisting of glass flux alone, which are shown in Table III above, were measured with a Mercury 2000, Series 1165, spectrophotometer of Datacolor (light type, D 65 , Observation angle: 10°). Color values of a 3 to 4μ thick coating of these decorative paints applied to a black glass ceramic (CERAN SUPREMA®) were measured. The unpigmented glass flux compositions were taken from DE 197 21 737 C1 (GF 1 ), DE 198 34 801 C2 (GF 2 ) and EP 460 863 B1 (GF 3 ). The color values are expressed as L* a* b* in the CIELAB system. 
         [0035]    So that the coating of the undecorated regions of a black glass ceramic panel is more distinguishable, according to a second embodiment of the invention, about 2 percent by weight of a black pigment (e.g. a Cr—Fe—Co—Mn spinel) with a maximum grain size of 5μ (D 50 &lt;2μ) can be added. Because of that the transparency of the black decorative paint is reduced, whereby the conspicuousness of the decorative paint is clearly increased on the glass ceramic. Without that the decorative paint looses its deep black color impression or is too rough. 
         [0036]    However with a zinc-containing glass flux, such as GF 1 , with more than 2 percent by weight pigment additive (e.g. at 2.7%), already a slight change of black color impression to a brown color was observed (when b* ≧−0.3 and a ≧+0.1 with L*=24). The continuous change of the color location, i.e. the increase of a* and b* values with increasing pigment fraction, was measured instrumentally. The color is increasingly “red’ and “yellow”, as seen in Table IV. The intensity of the black color impression of the decorative paint cannot be further increased simply by addition of more black pigment, because the brown color shade is observable with the eye when more than 2% pigment is added. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE IV 
               
             
             
               
                   
               
               
                 DEPENDENCE OF COLOR PARAMETERS OF THE 
               
               
                 DECORATIVE PAINT ON THE PIGMENT FRACTION 
               
             
          
           
               
                   
                 Color Parameters 
               
             
          
           
               
                 wt % Pigment 
                 Color 
                 L* 
                 a* 
                 b* 
               
               
                   
               
             
          
           
               
                 0 
                 Black 
                 23.6 
                 0.0 
                 −0.6 
               
               
                 2 
                 Black 
                 23.7 
                 0.1 
                 −0.4 
               
               
                 2.7 
                 Black-brown 
                 23.8 
                 0.1 
                 −0.3 
               
               
                 3 
                 Black-brown 
                 23.9 
                 0.1 
                 −0.3 
               
               
                 10 
                 Black-brown 
                 24.2 
                 0.1 
                 −0.3 
               
               
                 15 
                 Dark brown 
                 25.2 
                 0.2 
                 +0.2 
               
               
                 20 
                 Gray brown 
                 25.9 
                 0.1 
                 +0.1 
               
               
                   
               
             
          
         
       
     
         [0037]    The decorative paint, whose color parameters were tabulated in Table IV above, contains glass flux GF 1  (DE 197 21 737 C1) and pigment PG 1 , which is a Cr—Fe—Co—Mn Spinel. Pigment PG 1  contains 11% chromium (III), 15% Fe(II/III), 20% cobalt (II) and 20% Manganese (II/III). The decorative paint coating measured had a coating thickness of 3 to 4μ. The measurements were performed, as above, with a Mercury 2000 spectrophotometer, Series 1165, of Datacolor (light type, D 65 , Observation angle: 10°). 
         [0038]    However the brown color can be suppressed at overall pigment concentrations up to 3, or about 3, percent by weight is reached, when the black pigment (PG 1 , e.g. Cr—Fe—Co—Mn spinel) is re-melted together with a glass, which does not attack the pigment surface, and is subsequently ground fine (maximum grain size about 10μ, D 50 &lt;5μ). The glass used to make this at least partially coated or re-melted pigment PG 2  can, for example, be a zinc-free boro-aluminum-silicate glass. The proportion of the boro-alumino-silicate glass usually amounts to from 60 to 80%, while the coloring agent or pigment fraction in the at least partially coated pigment is from 20 to 40%. The pigment fraction in the decorative paint can be increased to about 3% by weight when using an at least partially coated “pigment” PG 2  comprising, for example, 70% by weight glass and 30 percent by weight coloring body, without producing a brownish color. That corresponds to 10 percent by weight of the at least partially coated pigment in the powdery paint mixture. Preferably the pigment fraction in the decorative paint amounts to 2.7% by weight, which corresponds to 9 percent by weight of the at least partially coated or re-melted pigment. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE V 
               
             
             
               
                   
               
               
                 COMPARISON OF COLORS OF DECORATIVE PAINT 
               
               
                 PRODUCED WITH NON-REMELTED BLACK PIGMENT 
               
               
                 WITH RE-MELTED BLACK PIGMENT 
               
             
          
           
               
                 Pigment Composition 
                   
               
             
          
           
               
                 Wt. %, 
                 Glass flux 
                 Pigment 
                 Color Parameters 
               
             
          
           
               
                 Pigment 
                 fraction 
                 fraction 
                 L* 
                 a* 
                 b* 
                 Color 
               
               
                   
               
             
          
           
               
                 0 
                 100% GF1 
                 0%   
                 23.6 
                 0.0 
                 −0.6 
                 Black 
               
               
                 2.7 
                  91% GF1 
                     9% PG2 
                 24.8 
                 0.1 
                 −0.6 
                 Black 
               
               
                 2.7 
                 97.3% GF1  
                 2.7% PG1 
                 23.8 
                 0.1 
                 −0.3 
                 Black- 
               
               
                   
                   
                   
                   
                   
                   
                 brown 
               
               
                   
               
               
                 Pigments: PG1: Cr—Fe—Co—Mn Spinel 
               
               
                 PG2: coated or re-melted PG1 (70% by weight glass flux, 30% by weight pigment - PG1) 
               
               
                 Glass flux: GF1 (DE 197 21 737 C1) 
               
               
                 Coating thickness: 3-4μ 
               
               
                 Spectrophotometer: Mercury 2000, Series 1165 (Datacolor), D 65 , 10° 
               
             
          
         
       
     
         [0039]    This latter decorative paint according to the invention has a color with lower a* and b* values, which are identical with values of the decorative paint made from unpigmented glass flux, as shown by the values listed in Table V below. Only the L* value is somewhat increased, i.e. the color is somewhat “grayer”, which however is still not observable with the eye as a weakening of the black color impression. The increase of the L* values is based according to the current knowledge on the burned-in boro-silicate-alumino-silicate glass, which strongly reduces the transparency of the decorative paint, so that the decorative paint on the black glass ceramic panel is more clearly observed than the unpigmented glass flux or the glass flux containing 2% pigment. 
         [0040]    Because of the deep black pleasingly lustrous appearance of the decorative paint on a black glass ceramic the glass ceramic surface decorated with a fine grid or pattern appears at first glance as if it had a structure or pattern (the decorative paint is not observed in its function as paint). The effect opens up new possibilities for design of the glass ceramic cooking surfaces. Of course the developed black decorative colors with a decorative pattern can be used as a so-called background texture, so that the glass ceramic cooking surface is provided with a very high quality design. The new decorative paint can thus be characterized as “texture paint”. The roughness Ra of the background texture is thus ≦0.35μ. 
         [0041]    The making of the glass fluxes for the decorative paint, their pigments and their application and the burning on of the decorative paint on the glass ceramic panel occurs according to known methods, for example as described in DE 197 21 737 C1. Explicit reference to this disclosure is made in the present application. 
         [0042]    The disclosure in German Patent Application 103 38 165.1-45 of Aug. 20, 2003 is incorporated here by reference. This German Patent Application describes the invention described hereinabove and claimed in the claims appended hereinbelow and provides the basis for a claim of priority for the instant invention under 35 U.S.C. 119. 
         [0043]    While the invention has been illustrated and described as embodied in a glass ceramic cook top having a cooking surface provided with a pleasing black decoration by applying a decorative paint to it, it is not intended to be limited to the details shown, since various modifications and changes may be made without departing in any way from the spirit of the present invention. 
         [0044]    Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
         [0045]    What is claimed is new and is set forth in the following appended claims.