Preparing a Crucible for melting metal
Before you use a crucible for the first time, it has to be "seasoned" or lined with borax. Put the crucible on a heat resistant surface. Heat the crucible until it starts to glow inside, then sprinkle borax powder into the bowl. Heat the borax until it melts and swirl it to completely cover the inside of the crucible.
Add more borax and heat it if necessary.
Put the crucible aside in a "slow cooling pot". One suggestion is - use an old cast iron pan or pot. Put some small pieces of pumice or crushed charcoal in the pot for the crucible to rest on. Vermiculite is another subtance that can be put in the pot. Avoid subjecting the crucible to very rapid changes of temperature. It can shatter.
The inside the crucible will look like glass when the bowl of the crucible is fully covered and if the borax was melted properly.
When you use a crucible, pre-heat if before adding the metal. Heat the metal and before it melts, add borax borax powder or flux. If you add the flux too soon it expands and blows away with the gases from the torch.