Glen, what is your opinion on the use of saddle soap as the only cleaner and conditioner used on a shoe? Shoes made out of heavier leathers (cowhide) such as Horween's Dublin leathers, often come with the recommendation that saddle soap should be used for the care of the shoe, and that it is the only thing necessary. Additionally, the container (I use Fiebing's Saddle Soap paste) says that it "cleans leather and lubricates the fibers to prevent brittleness, all while maintaining suppleness and strength", and it "cleans and polishes in one easy step." They recommend using a damp cloth or sponge to create a lather and applying it to the leather, then allow it to dry, then buff with a soft cloth or brush for a light sheen. Fiebing's seems to have a stellar reputation, and they have been around for quite some time. I know Cold Iron says that he only uses the 100% glycerin saddle soaps on his shoes that recommend this type of care. I've always just followed the manufacterer's instructions on the use of saddle soap and haven't had any trouble, but I was wondering if you have some insight given your "molecular" approach to leather cleaning and care. There are many theories (I disagree with almost all of them) about saddle soap in the forum and how it will destroy your shoes, and I am hoping you may be able to give some conclusive data on the argument.
I will give it a try:
Saddle soap typically comes in a tin with a mixture of glycerin, wax, and oil, with oil being the much smaller ratio. Glycerin is a fatty based soap and is milder than most soap, but it does contain sulfides, which cause the foaming. The sulfides in soap are also what cause soap to irritate your skin when not washed off.
Sulfide is an anion of sulfur in its lowest oxidation state, and it is sulfur that causes sulfuric acid to be so much stronger than hydrochloric acid.
Another aspect of glycerin is that it is a humectant that is capable of drawing moisture towards itself and trapping the water molecules, not something you want to happen in your shoe leather.
The idea of applying saddle soap as wet foam, and then brushing the shoe off when it is dry, is that the majority of the sulfides will dry as a film on the surface of the leather and be wiped off with a brush or cloth. The remaining oils would then theoretically balance out any remaining sulfides, as well as lubricate the leather.
The more critical aspect of using saddle soap is the water application. Water will push oil out of shoe leather. How much oil gets pushed out depends on a number of factors like how much water is used in relation to the thickness of the leather, and how much oil is in the shoe, or reintroduced into the shoe. This is why saddle soap works better with thicker boot leather, than thinner shoe leather.
For all the reasons above I would not recommend saddle soap for leather shoes, however I think that the thicker leather of boots would probably do fine with it, and is probably a quicker and cheaper way to keep boots clean.
All of these issues are minuet issues, but given a choice, I would prefer a cleaner/conditioner to saddle soap.