Viscosity is related to temperature. Hmm, Having just skipped through all the above I find it difficult to agree with how 'annealing crack' is being defined. Whilst it may be that there are cracks in Monart are due to poor annealing, it seems to me that any cracks that occur. This is an issue when we are below the annealing point - and I will discuss annealing below. Suffice it to say, that cooling needs to be slow enough that the glass cools through and through in a homogeneous fashion. None have come up with a fulproof way of repairing cracks (or in other glass for that matter which is why as a dealer I avoid damage, but as a collector I may entertain it. I own damaged items because I get enjoyment from them aesthetically and/or because they are rare. Luckily, most display in such a way as to avoid the damage! I have, in the past taken cracked Monart to restorers. Thermal Shock This happens if glass is heated or cooled too quickly. The glass cracks immediately when this occurs. Thermal Shock When Heating: when glass is heated from room temperature gran turismo 5 update usb up to fusing temperatures, the molecules gain energy and the glass expands. In that case, you may drop the glass and cut your hands. This may cause a traumatic crack as well - as demonstrated in the photo at the very top of this page! This occurs at a viscosity of 107.6poises. Annealing point : The temperature at which strain in thin sections will be removed in 15 minutes and which viscosity is 1013 poises. The strain point is that temperature below which permanent strain cannot be introduced. My advice to collectors has always been to buy if you like the item and if you don't hope for an increase in value. My advice to investors, or collector's with an eye for investment is, do not buy damaged items - however that damage. The seminar will consist of advanced topics that will provide an in-depth look key issues related to breakage. The critical focus will be on the practical workshops using advanced fracture analysis techniques and thoroughly detailing findings.