First of all, you soak the gherkin slices in a cold wet brine overnight. The brine consists of 2 oz salt dissolved in 1 pint water. The salt must be pure sea or rock salt, i.e. not contaminated with anti-caking agent.
Next day, rinse very well and leave to drain. Pack into cold sterilised jars, cover with spiced vinegar, and seal.
Last time, I simmered the gherkins in the brine for 10 minutes. As a result, they went too soft. This time, I am going to add some sugar in the hope that this will make them more palatable.