Pat asked about soft soap. This is a soap made from animal fats and potassium carbonate reaction - the soap is essentially potassium salts of fatty acids. It is a very soft gel which does not set. If your forebears in the US were pioneers, then this is what they had for their own home-made soap, the source of the potassium being woodashes (hence potash). Ordinary hard soap is the similar reaction of sodium carbonate (washing soda) with animal fats. The better "quality" soaps contain larger amounts of the glycerin which is the other product of the alkali + fats reaction. Glycerin acts as a moisturizer and some cosmetic preparations contain it though it is probably not used as much as it used to be. The problem with high levels of glycerin is that the soap takes longer to set. The soap bars you use today still contain about 27% water, otherwise the sodium salt based soap would be too hard and difficult to lather (notice how the last fragment of the bar never lathers so well? - its too dry). The only trade name for soft soap I know is Swarfega and this may be a UK name only. However, ask any mechanical engineering friend. If he/she forgets to use a barrier cream, he/she will probably use a soft soap to wash off the oily grime afterwards. The soft soap is acting as a spreader but also has some insecticidal properties of its own. Definitely do not use a detergent. Diana mentioned using baking soda with a spreader to combat mildew and black spot. Sodium bisulfite is more powerful. If any of your friends do any of their own brewing or fermenting, they will use sodium bisulfite to sterilize their bottles, etc., so this material is readily available from any home beer- or wine-making kit provider. I don't have the recipe ready to hand but I'll pass it on when I find it. Sodium bisulfite is much stronger than sodium bicarbonate (baking soda) so if you try your own experiments start at the dilute end! Essentially it works by producing low concentrations of sulfur dioxide. One of the noticeable effects over my gardening lifetime is the way in which the reduction in air pollution has allowed black spot to return and infect roses much more. Put it another way - when the air was polluted with sulfur dioxide, black spot on roses was very rare. Mildew was similarly affected. Enough of your chemistry lesson for today. Regards to all Hamish