In this case I want the hair to all fall out easily without dissolving, so I cannot use lye or sulfide, but I need a good slip. I heard so much about how pH alone will cause slip, so I decided to try it. I'm disappointed.
Does high pH alone cause slippage?
Soak down 2 iffy/decent air-dried pelts for 6 hrs. in hot water with a little degreaser added (pH 8.5 of degreaser, water overall pH 7.5-7.6).
No slip other then what was already occuring on the pelts at time of acquisition. Longer study needed.
Skins moved in to conventional soaking vat where they were placed in a solution of 12 oz. sodium bicarbonate, 10 gal. water, and 1/2 ounce degreaser. pH 9. Temp. 70-75F. Stir 3x/day.
Results at 48h:
NO SLIP. Yes, I pulled on the hair to check and it didn't come out. Leather is very thick. Faint bad smell.
Conclusion: Mild raising of the pH is not sufficient to slip hair, even on a grossly mishandled skin - see above (air-dry skins with known bad areas, hot water soaks, scrub, extended soaks with no bacteriacide, high pH, no salt). Caustic chemicals such as sulfide or hydroxide are needed to obtain a good slip.
Bacteria or "taint" or "green belly", and over-shaving, remain the main causes of slip spots.
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In hair-off tanning you use hydrated lime or an alkali (lye) to remove the hair. Lye has a pH of between 11 and 14. A strong soap will have a pH approaching 12. Your soap is too weak and would likely cause slippage from bacteria before the pH became a factor. Either way, the slippage would be haphazard and not as uniform as an alkali product would have done.
Why the "pH" is the cause of slippage? We hear all the horror stories about using soap to wash a cape and the hair starts to slip. But we so often neglect the handling of the skin before the washing. It is a fact that some of the ingredients in "soap" can cause a skin to slip. I believe Glen and OS have pointed out that sodium hydroxide is one of the big culprits as well as "SDS".
Here is what I believe. When you wash a cape in a higher pH bath after the pickle, you are mixing a strong acid with a strong base. Major (violent) reactions are bound to happen and cause some cell/structure damage! This no doubt does happen over the entire cape including the hair follicle. This can Easley be seen when you add a pickled cape to the buffering solution. You should see small bubbles all over the cape. The same thing happens when you add baking soda (bicarb) to your pickle to neutralize it (foams up and fizzes). I believe the chemical reaction that happens in and on a cape in a higher ph bath is not unlike millions of small bombs going off on, and in the cape. I see this as a sure fire way to cause damage!
Later taters! Joe
An acidic pH has the propensity to shrink animal tissue. We call it "pickling", but it locks and seals the protein, thereby locking in the hair. With a base/alkali/high pH chemical, it destroys protein which is why it is so great at dissolving grease. The hair follicle is the weakest link in this system, however, and it gets attacked first allowing the hair to fall out and the outer epidermal layer to dissolve.
Remember, contrary to what you explained, when you mix a "strong" acid with a "strong" base, you end up with glorified water (not really, but a chemical that is at the midscale of the pH meter.
MOST IMPORTANTLY, remember these are laymens terms and examples. Chemistry is certainly a little more involved than our descriptions and guy's like Glen can slam dunk most of this with explanations that go far beyond what you and I discuss. He must get tired of "talking down" to our level sometimes. LOL.
Yes! "locks and seals the protein" AKA "fixes". Sounds kinda like "tanning" fixes the "skin"
What I was trying to explain is: The chemical reactions taking place in and on the skin are also taking place in the cells them selves. As well as between the hairs and the cologan structure.
Here is a simple test of what I am talking about. Take a zip lock bag, fill it with your pickle. Then add a small amount of soapy water mixed in the same way you would mix a soap bath for washing a cape. Seal the bag and set it in a plastic bucket (use the plastic bucket for saftey). How long doe's it take to wash a cape? 5 or 10min? It only takes about a minute or less to cause the zip lock bag to burst!
Most of the lipid structure of the cell is allready destroyed after the the cape is put in the pickle. But you said it your self "The hair follicle is the weakest link in this system" So this is where you "see" the most dammage (hair slip)
As allways George, Your info is vallued and appreciated.
I know that when you mix an acid with a base you will get a neutrel solution provided they are about the same strenth. I don't belive the end result is what causes the dammage but rather the transisson between the two. Like the leter A is acid and the leter Z is the base and M or N is "glorified water" it is the A-M or Z-N reaction that is the culprit. Again just my thoughts. Joe