This section is from the book "The London Art Of Cookery and Domestic Housekeepers' Complete Assistant", by John Farley. Also available from Amazon: The London Art of Cookery.
Your walnuts must be taken from the tree before the shell is hard, which may be known by running a pin into them, and always gather them when the sun is hot upon them. Put them into strong salt and water for nine days, and stir them twice a day, observing to change the salt and water every three days. Then put them into a hair sieve, and let them stand in the air till they turn black. Put them into strong stone jars, and pour boiling vinegar over them. Cover them up, and let them stand till cold. Then give the vinegar three more boilings, pour it each time on the walnuts, and let it stand till cold between every boiling. Then tie them down with paper and a bladder over them, and let them stand two months. Having stood that time, take them out of the vinegar, and make for them the following pickle: To every two quarts of vinegar, put a quarter of an ounce of mace, a dram of cloves; of olack pepper, of Jamaica pepper, ginger, and long pepper, an ounce each, and two ounces of common salt. Boil ten minutes, pour it hot on the walnuts, and tie them down, covered with paper, and a bladder. This quantity of spice, is intended for three hundred walnuts.
Having procured a sufficient quantity of walnuts of the largest size, and taken the above precautions that their shells are not hard, pare them very thin till the white appear, and throw them into spring-water, with a handful of salt. Let them stand in that water for six hours, and put a thin board upon them to keep them under the water. Then set on a stewpan, with some clean spring-water on a charcoal fire. Take the nuts out of the water, put them into the stewpan, and let them simmer four or five minutes, but not boil : have ready a pan of spring-water, with a handful of white salt in it, stir it till the salt is melted, take the nuts out of the stewpan with a wooden ladle or spoon, and put them into the cold water and salt. Let them stand a quarter of an hour, with the board lying on them to keep them down as before ; for if they are not kept under the liquor they will turn black.
Then lay them on a cloth, and cover them with another to dry; carefully rub them with a soft cloth, and put them into the jar, with some blades of mace and nutmeg sliced thin. Mix the spice between the nuts, and pour distilled vinegar over them. When the jar is full of nuts, pour mutton fat over them, and tie them close down with a bladder and leather, to keep out the air.
Having gathered the walnuts with the same precautions as above directed, put them into strong vinegar, and tie them down under a bladder and paper to keep out the air. Let them stand twelve months, then take them out of the vinegar, and make for them a pickle of strong vinegar. To every quart, put half an ounce of Jamaica pepper, the same of long pepper, a quarter of an ounce of mace, the same of cloves, a head of garlic, and a little salt. Boil them all together five or six minutes, and then pour it upon the walnuts. As it gets cold, boil it again three times, and pour it on the walnuts. Tie them down with a bladder and paper over it; and if your vinegar be good, they will keep several years, without either turning colour or growing soft.
 
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