Here is a "recipe" I found and posted on Orchid before:
You can change the amounts in proportion to you batch size.
If you need help ask me.. This is from an agricultural source.
A combination of hydrate lime (CaO) mixed with sulfur. Lime sulfur
is extremely water soluble, but incompatible with other pesticides
due to it's alkaline reaction when diluted with water. It should be
used by itself.
Lime sulfur can be made by combining 20 pounds of rock lime and 15
pounds of flowers of sulfur with 50 gallons of water. Place in a
large iron kettle or boiler outside (this stuff smells!) and boil for
one hour. Allow to cool and settle. The clear, amber fluid
remaining after filtering is lime sulfur. It's probably cheaper and
easier to purchase a prepared product. This stuff is a pretty
plant fungicide .
My comments; The "recipe" may be a little confusing .. I take rock
lime to be calcium carbonate (CaCO3 ) Kilned lime or burnt lime
will be calcium oxide ( CaO ) which becomes slaked lime - calcium
hydroxide - hydrated lime (CaOH) when mixed with water. I don't see
any "magic" in the chemistry although I would be most likely use a
burnt or kilned lime which is more alkaline. All components
available either at a garden supply or in the concrete materials
area for the hydrated lime. A 50 # sack is about $4.50. Excesses
can go thinly on the lawn or garden especially east of the
Missisippi river in the US. DO NOT ACIDIFY as this makes hydrogen
sulfide (H2S) Rotten egg smell. This is a toxic gas.
Like everything be careful. And the Recipe is scalable - a batch
doesn't have to be that big!