In a message dated 7/5/2004 2:01:11 PM Eastern Daylight Time, "Mike & Jackie" <warrior02@...
>I am working on my Menpo, and I decided to use thick leather rather
>than metal or Polyethelyne, it worked well, and the nose shaped
>good, but I am wanting to harden the leather a bit more, the last
>time I tried, I tried cooking it, it worked but it shrank some, and
>was too brittle,
>anyone have any ideas??
Well, a quick question is are you treating the leather in any way when you work it?
First I will digress into the ways, then point out the Japanese ones.
Leather can be stiffened by imersion in water and then drying quickly
(low heat, not cooking the leather) What happens is the water pulls with it some of the natural oils and also promotes shrinkage of the cells. This results in the leather being a hair smaller, slightly thicker, and more stiff. Disadvantage, wetting the leather instantly removes the stiffness. Also the removal of the natural oils accelerates the dry-rot process.
Wax hardening: by utilizing a wax one raises the temperature of the wax until liquid and uses it to fill the natural voids in the leather, thus increasing perceived stiffness when the wax cools. A benifit is this nearly eliminates the chance of dry rot. (The wax keeps the natural oils from evaporating.) However a drawback of this is as the temperature of a finished piece rises, the wax softens and stifness is lost. Also in very, very cold conditions, the slight amount of water in waxes may cause the wax to expand, thus tearing the fibers of the leather and causing failure (in sub zero conditions it can become brittle)
Heat hardened leather. By application of heat (high heat, cooking the leather) one actualy causes the leather to "cook" water is removed and the oils break down into the fibers. this results in a stiffer fiber of the leather, however the oil breaks down rapidly and will come to a point where it evaporates in a very narrow temperature window. This means the leather is dry and brittle (dry rot)
Water boiled leather: esentualy the same as water hardened, except higher teperature, an amalgimation of heat hardened and water hardened. In this the water acts to regulate teperature to keep the window more controlable. Also the oils as they break down must be exposed to air to evaporate, in water they cannot. Also as the porosity and voids in the leather close from the fibers expanding, there is less chance of the oils evaporating over time. This causes the thickness to noticably increase, though there is a good amount of shrinking. Disadvantage is it must be cared for with oils, which will soften it slightly over time. Also the shrinking factor means that articles you want hardened have to be designed that way from the outset. It is also hard to work, and after it drys/cools is a real bear to work with.
Wax/oil boiled leather is much the same as water boiled leather the temperature is slightly higher and further causes shrinkage and thickening. Flexibility of the leather is nearly nil, to take the most advantage of this the leather should be for relitively flat pieces, and start with thick leather. (thin leather tends to warp and stress itself in the process of hardening to the point of developing weak spots. Also even while hot it will not want to bend easily and very difficult to dish. I used standard vegtible taned belt leather (about 1/8 inch thick) to make knee cops, however I made them and sandwiched them in sheet steel moulds before giving them the deep-fry (joke) dunk. they are now almost a 1/4 thick and almost too small to be used for elbows. however one got run over by the car and it did not deform.
The other approach (japanese) is resin. Impregnate the leather with a resin, and when it drys it will harden. the benifits are very durable, waterproof, heat resistant, and pretty light weight. (the moisture content is way down. It will not dry rot. Most of the time it is impossible to make mildew or get slimy. the down side is it is a bear to work when dry, and traditionally it uses japanese lacquer wich is very very very unpleasant to work with. (think posion ivy) Modern resins like polyureathane sometimes will react with the leather and cause its fibers to desolve. You must find just the right kind. (something I have worked on, without alot of success) I'm sure it can be done, but much experimenting needs to be done. Also it is messy as all get out. (very few resins are liquid enough to be absorbed well into the leather, therefore they must be worked in. Japanese lacquer has the benifit of taking forever to dry, however even slow drying polyurethane starts setting up after a couple of minutes and is then too thick. I have been looking for a resin that one can heat up to thin that once dry will not soften under heat. (Looking at wood bonding resins, might be some promist to them, my experiments are on hold for now.)
How to solve the problem of the mempo? I do know know other than maybe real japanese laquer, which I do not reccomeend for people to work with.
Other than that, maybe you can get some ideas from above.
Note: Japanese lacquer (ushuri (sp)) is "distilled" in much the same way as maple surup is made but from the relitive of posion sumac. I am immune to posion ivy and the laquer will break me out as bad as other people. It is only dangerous in it's liquid form, once the water evaporates and it is hardened it is an excellent coating. It is even slighly tolerant to petrochemicals. Warning, fine dust from sanding lacquer or polishing it can cause severe respitory distress in people with alergies or lung/bronchial conditions. Please use common sense and a mask while doing any sanding or at the very least good airflow out-of-doors.