This morning my tarpaulin was full of water from overnight rain and the timbers holding it up were bending alarmingly under the weight.Now my rate of progress on the carving starts to slow as I have to proceed with more caution in order to get an even thickness in the stone. I have done this before in marble but the tensile strength of onyx is very poor and I dare not take it too thin. In the picture you can see the depth marks showing me where I need to remove more material and where to stop. Ten is more than thick enough but five and a half is probably already a bit thin. The strength of the form is helped by its undulations of course giving it the sort of strength an eggshell gets from its shape. You can see my wooden callipers which have been mended many times.