<HTML><HEAD><TITLE>clayart - thread 'crazing problem (translation needed)'</TITLE></HEAD> <BODY bgcolor="#FFFFFF" leftmargin="100"> <img src = "small%20potters%20logo.gif" align="right"> <H2><font color="#000080"size="6">crazing problem (translation needed)</font></H2> <H3>updated wed 18 oct 00</H3> <p>&nbsp</p> <H3>Denis Caraty on tue 17 oct 00 <font size="3">(<A HREF=MailTo:dcaraty@GIEN.COM>dcaraty@GIEN.COM</font></A>)</H3> <blockquote>  <BR>J'ai fait plusieurs calculs sur vos glacures : <BR> <BR>1)T.E.C <BR>REV C   : 59.00 x 10-7 <BR>CR#4    : 49.26 x 10-7 <BR>Canadore        : 58.25 x 10-7 <BR>Cela confirme vos calculs sur le coeeficient de dilatation. <BR> <BR>2)Melting Temperature <BR>REV C           : 1234?C (^6) <BR>CR#4            : 1209?C (^5) <BR>Canadore        : 1073?C (^3) <BR>La glacure "Canadore" est "over fired" si vous cuisez ^6 ou ^7. <BR>Cette glacure est donc tres active pendant la cuisson, elle se comporte <BR>comme un puissant solvant des elements contenus dans la pate de vos <BR>produits. Elle s'enrichit avec les composants de la pate (SiO2 en <BR>particulier) et ses proprietes sont modifiees. Sa couche superieure est sans <BR>doute restee normale, mais sa couche inferieure en contact avec la pate est <BR>differente. C'est ce que certains d'entre nous appellent "la couche <BR>intermediaire". <BR>Apres cuisson, elle resiste mieux au "crazing test" car ses proprietes <BR>mecaniques ont ete renforcees et qu'elles sont plus progressives dans <BR>l'epaisseur de la glacure. <BR> <BR>Votre pate a donc probablement un coeficient de dilation inferieur ou egal a <BR>celui de vos glacures. <BR> <BR>Vous pouvez tester l'effet "couche intermediaire" sur la glacure REV-C et <BR>CR#4 en comparant ces deux glacures cuites une seconde fois dans votre four <BR>a ^6-7. Apres une deuxieme cuisson elles seront plus resistantes, car la <BR>dissolution de la pate au contact de vos glacures aura ete augmentee. <BR> <BR>Denis Caraty <BR>Societe : Faienceries de Gien <BR>78, place de la victoire, 45500 Gien, FRANCE <BR>Fax : (33) 2 38 67 92 36 <BR>dcaraty@gien.com <BR>http://www.gien.com <BR> <BR> <BR>-----Message d'origine----- <BR>De : Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]De la <BR>part de Les Wright <BR>Envoye : lundi 16 octobre 2000 22:04 <BR>A : CLAYART@LSV.CERAMICS.ORG <BR>Objet : <BR> <BR> <BR>I'm having difficulty understanding the relationship between the coefficient <BR>of expansion of the clay body and that of the glaze. The glaze calculation <BR>program that I use in determining expansion numbers is Insight and the <BR>expansion numbers of oxides and materials used are those provided by Ron <BR>Roy. <BR> <BR> <BR>It is my understanding that Ron uses a dilatometer to measure the expansion <BR>of <BR>all the clay bodies that Tucker's sells and I have all these figures. Using <BR>Insight, I can calculate the attendant glaze expansion. <BR>Trough reading C.W.Parmelee and a couple of other sources, supposedly glaze <BR>fit (no crazing, but good compression) should fall within 10% to 20% less <BR>expansion than the clay body with 15% being optimal. I have lowered my <BR>original clear glaze from c.o.e # 445.51 to 295.76 and yet it is still <BR>crazes. <BR>Obviously, I will keep lowering the c.o.e until the crazing disappears, I <BR>don't know any other way of solving the problem. Does it have anything to do <BR>with measured vs calculated and are the c.o.e numbers given for oxides and <BR>materials so inexact that mathematical comparison is useless. And yes, I <BR>know, <BR>test-test-test! <BR>I have rambled on far too long, in short, I need a great deal of help. <BR> <BR>This is the original and adjusted version of the glazes above. I fire from <BR>about c/6 to c/7 and use Orton standard cones in oxidation. I use Tucker's <BR>MCS, but I have also tested these glazes on Pottery Supply House 910; <BR>Tuckers's Smooth White, Mid Smooth Spec, 650, Mid Porcelain Five. <BR> <BR>Two Recipes: REV C & CR#4 <BR>=========================================== <BR> G-200 FELDSPAR G200.   32.00  16.00% <BR> WOLLASTONITE........   28.00  14.00%     29.29  14.65% <BR> F12 (FERRO3134).....   24.00  12.00%     22.78  11.39% <BR> STRONTIUM CARBONATE.   20.00  10.00%      3.45   1.72% <BR> TALC................    4.00   2.00%      6.51   3.25% <BR> EPK KAOLIN..........   48.00  24.00%     55.25  27.62% <BR> SILICA..............   44.00  22.00%     63.20  31.60% <BR> CADYCAL.............                      8.14   4.07% <BR> MAGNESIUM CARBONATE.                     11.39   5.70% <BR>                     ========          ======== <BR>                       200.00            200.00 <BR> <BR>                    CaO  0.53*  9.30%      0.57* 10.83% <BR>                   MnO2  0.00   0.00%      0.00   0.01% <BR>                    MgO  0.07*  0.90%      0.32*  4.37% <BR>                    K2O  0.07*  1.94%      0.00*  0.13% <BR>                   Na2O  0.10*  1.90%      0.06*  1.36% <BR>                  Fe2O3  0.00   0.22%      0.00   0.25% <BR>                   TIO2  0.00   0.08%      0.00   0.09% <BR>                   B2O3  0.14   2.98%      0.21   4.99% <BR>                  AL2O3  0.41  13.14%      0.34  11.74% <BR>                   SiO2  3.31  61.97%      3.20  64.88% <BR>                   P2O5  0.00   0.03%      0.00   0.03% <BR>                    SrO  0.23*  7.54%      0.04*  1.33% <BR> <BR>                COST/KG  2.52              1.88 <BR>                  Si:Al  8.02              9.40 <BR>                 SiB:Al  8.35             10.02 <BR>                 EXPAN 445.51            295.76 <BR> <BR> <BR> <BR>PS: Here is a glaze that appears to be crazless on all the aforementioned <BR>clay <BR>bodies and its c.o.e is 426.23. <BR>Go Figure! I test for crazing by submersing my glazed tiles into 20*cent. <BR>Water after heating them in an oven by 50*cent increments with the started <BR>point of 100*cent. Please explain why and how this can be so. <BR> <BR>RED TEM C/6 CANADORE (STEVE) <BR>TA = TEM REV A <BR>============================================ <BR> F12 (FERRO3134).....   12.00   5.08% <BR> TALC................   36.00  15.25% <BR> SILICA..............   52.00  22.03% <BR> CADYCAL.............   34.00  14.41% <BR> F-4 FELDSPAR........   62.00  26.27% <BR> BELL DARK BALL CLAY.    4.00   1.69% <BR> BENTONITE...........    4.00   1.69% <BR> RED IRON OXIDE......   32.00  13.56% <BR>                     ======== <BR>                       236.00 <BR> <BR>                    CaO  0.41*  6.89% <BR>                   MnO2  0.00   0.03% <BR>                    MgO  0.41*  4.90% <BR>                    K2O  0.05*  1.34% <BR>                   Na2O  0.14*  2.58% <BR>                  Fe2O3  0.30  14.41% <BR>                   TIO2  0.00   0.03% <BR>                   B2O3  0.40   8.35% <BR>                  AL2O3  0.21   6.37% <BR>                   SiO2  3.06  55.10% <BR>                    SrO  0.00*  0.01% <BR> <BR>                COST/KG  1.60 <BR>                  Si:Al 14.70 <BR>                 SiB:Al 16.63 <BR>                 EXPAN 426.23 <BR> <BR>Notes: <BR>THIS RECIPE FROM CANADORE ELIMINATES GERST BOR BY SUB CADY CAL. RED IRON IS <BR>FORCED PHANTOM. <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR>____________________________________________________________________ <BR>Get your own FREE, personal Netscape WebMail account today at <BR>http://home.netscape.com/webmail <BR> <BR>____________________________________________________________________________ <BR>__ <BR>Send postings to clayart@lsv.ceramics.org <BR> <BR>You may look at the archives for the list or change your subscription <BR>settings from http://www.ceramics.org/clayart/ <BR> <BR>Moderator of the list is Mel Jacobson who may be reached at <BR>melpots@pclink.com. <BR> </blockquote> <BR> </BODY></HTML> 
