The Forresters

Can anyone tell me how to treat black olives so that they are suitable for eating and cooking (not pressing). I've got a recipe that uses 30% sodium hydroxide, but I can't find anywhere to buy it. Other books talk about soaking in brine, but give no details of quantities of salt. Our olive shrub (it's not a tree) in the Deux Sevres is quite young and our crop this year is only about 700g, but I can't bear to waste them. A really clear, tried and tested recipe would be wonderful. Also any advice on pruning and general treatment of the shrub. Thanks Judith