Briefly discuss two methods ofobtaining a glaze on ceramicmaterials. Give the advantages anddisadvantages of both methods.

Briefly discuss two methods ofobtaining a glaze on ceramicmaterials. Give the advantages anddisadvantages of both methods.

1. Glazing can be done using an Overglaze powder mixed with Stain and Glaze Fluid and fired at the same temperature as the 1st dentine firing (880⁰C) in air rather than firing in a vacuum, for 1 minute.

   • Advantages-
     • Uses a lower temperature which unlike self-glazing reduces the risk of deformation/ pyroplastic flow.
   • Disadvantages-
     • Over glaze can enter perikymata/grooves carved into the tooth filling them in and losing the aesthetical addition.
       • if the glaze pools in certain areas it may lead to discolouration.

2. Alternatively glazing may also be completed without using an Overglaze, by firing the crowns in air for 2 minutes at 880⁰C.

   • Advantages-
     • During the process the surface of the porcelain melts and fuses just enough to fill in the slight surface irregularities or porosities.
   • Disadvantage-
     • This may cause the crowns to change shape and be slightly rounded if kept at this temperature for too long
       • If the porcelain is held at too high a temperature or hold under heat for too long, the porcelain can slump (undergo pyroplastic flow)
         • the restoration can lose natural contours, recrystalise, and become opaque(devitrify).
   • Self-glaze is exposed to temperatures high enough to permit porcelain to fuse together and create a smooth, glossy outer skin. It uses atmospheric pressure instead of vacuum.