[thedoc (OP)]

Many years ago, I was obliged to polish to a mirror finish the leather shoes and belt of a certain sergeant to a mirror finish.  The only way of achieving the desired result was to use copious quantities of spit, a trick which was taught to me by various people who had spent time in the army.  My question is ... why does spit enhance the shine of shoe polish?  And perhaps a related question ... modern shoes don't seem to require polishing. What surface finish is applied in the manufacturing process which gives an everlasting shine?

Asked by Dave, South Africa

                                          Hear this Question on our Podcast

[thedoc (OP)]

We put this to Chris Powley-Williams, Leatherwise in Northampton, UK:

[img float=right]http://www.thenakedscientists.com/forum/copies/RTEmagicC_450px-Bull_polished_drill_boots.JPG.jpg[/img]We're quite intrigued by the question posed by Dave as to why spit and polish is so successful on your shoes. The reason is all to do with protein. Traditionally in the leather industry when we wanted a very highly glazed or highly polished shoe we used to use the protein that you find in milk and that's casein. It would have been applied to the leather surface and it would have been fixed in place with formaldehyde or formalin, some people would know that as. The we would have used a glass block and glazed the actual finish and that would have given you this high polish effect. In effect that's what Dave is doing every time he spits on his shoes. In your saliva there's a high amount of protein. By spitting on your shoes and then rubbing it up to a polish you're actually trying to glaze the protein in the same way we would have done traditionally, many years ago. He then poses the question, well nowadays how are finishes different? We tend not to use the protein finishes. They're very brittle. We're not allowed to use formaldehyde the in the same way we used to use it and so we tend to use a lot of polymer finishes and nitrous cellulose, polyurethane, things like that. We can achieve the same levels of gloss but in quite a different way. One interesting fact we came across ourselves was that actually it's best to clean your shoes when you're happy, the reason being that the protein in your spit or saliva actually decreases if you're feeling depressed and increases when you're feeling happy. If you want a really good gloss on your shoes only spit on them when you're in a good mood. That should solve all your problems.

[chris]

Does the spot not just act as a lubricant helping you to sand down the surface more finely like wet and dry paper?

[JnA]

Scuba divers use spit to stop their mask from fogging up...



.. that's all I got.

Maybe there's a correlation there?

[Chemistry4me]

Natural leather usually has a shine that does not gleam in bright light. Depending on the tanning technique and chemical treatments applied to the leather, however, natural leather can have the gleaming shine of patent leather items. The little bit of dullness found in shoes made with natural leather is caused by the pores that allow the material to breathe. Imitation leather like patent leather are made from plastics, vinyl, and other synthetic compounds. Imitation leather is shinier and more opaque compared to natural leather, and resists stains and weather better. The problem with imitation leather is that the exterior tends to flake over time, especially if you use the shoes a lot.

[Chemistry4me]

Enzyme(s) in spit enhances the shine?

[erickejah]

spits are not just used in objects.ψ