A new design of frying pan is made from glass ceramic 9606, a material with excellent thermal shock resistance originally developed for missile radomes. The pan bottom is \(4.2 \mathrm{~mm}\) thick. When placed on a gas cooker with a pat of butter in it, it is observed that it takes 7 seconds before the butter starts to melt. Use the rules of thumb of Chapter 2, Engineering Materials and Their Properties and this chapter 3 to estimate, first, the thermal diffusivity of glass ceramic 9606, and from this, its thermal conductivity.