To get perfect crackling you first need to boil a jug of water and pour the boiling water over your scored pork skin.
Then your pork skin must be completely patted dry with a paper towel. Once dry, your skin should be rubbed with salt and a little pepper.
This process opens up the pores in the skin allowing the skin to dry and bubble when exposed to high heat!.
The next secret to perfect crackling is to make sure your oven is pre-heated to the maximum temperature, lets say 250 degres celcius. You should then place your prepared pork roast in the oven for at least 20-30 minutes before turning your oven down to cook at 180 degres for the remaining duration cooking time!.
This process should ensure almost perfect crackling every time.