I’ve got some questions that are both more in depth about tanning and more superficial as well: On a molecular level, how are chromium and polyphenols (tannins) interacting with the collagen matrix? Are they bonding to the same or different sites? Are aluminum and chromium bonding to the same sites, but chromium just is able to form more ligands than aluminum? Are you able to illustrate what’s happening in a simplified way? (Edit: went back to the old video kzbin.info/www/bejne/rGqqip96f9iqaqM and see that chromium is bonding to the carboxyl groups in collagen then bonding to other chromium molecules to form a polymer network) With regard to shell cordovan, my understanding is that shell is a hyaline cartilage membrane, meaning it is primarily composed of type ii collagen and chondroitin sulfate whereas most leather is made from skin which is primarily type i collagen. Does the chondroitin play any role in the different characteristics of shell (is this eliminated during bating as well) or is it more the different chain structures between the types of collagen? Is it fair to summarize the advantage of hot stuffed leather compared to fat liquored leather as having both more volume of fat and more fats that are typically insoluble in water? Is it as simple to say the advantage of using these fats is just the difference in textures between oil vs. tallow/lard/animal fat vs. beeswax? I think one take away from the 101 course is that leather is the end result of hundreds of different decisions to answer the question of “what do you want to make?” Can you connect the dots as to how all of the following statements could be true over time: “If I want to make razor strops, then I should use shell cordovan.” “If I want make gaskets, then I should use chromexcel.” “If I want to make winter work boots then I should use shell cordovan.” “If I want to make boots for marines fighting in Africa then I should use reversed cxl or waxed reversed cxl.” Through history, what to make with these leathers has changed, though the leather hasn’t. I guess the question in there is, if you started from scratch and you said “I want to make boots” would the end result still be these tannages, or would you maybe create or use a different product? Or does that question just lead to the question “what kind of boots?” Or is it more like “let’s make this awesome leather and no matter what it’ll find a home because it’s awesome?” Specific to Esteban: What are your favorite leathers to make at Horween tannery? What are your favorite leathers to use? Are there any leathers from other tanneries that you respect/like in terms of how they look, feel, or are made on a technical level? It seems like you could point to dozens of different individual decision points that would make Horween leather unique, from the chemist’s perspective, what is the overarching guiding philosophy behind those decision points? Would also be great to hear what Phil and Nick think.

Guest Request: Tony Medlin, Chicago Bears equipment manager - kzbin.info/www/bejne/gJrMo5mOpcuEpK8feature=shared. He’s probably about to be very busy, but he’d be a cool person to talk to about football leather and performance footwear amongst other things. I’d also love to see Horween Tannery pop up in the b roll for this season’s Hard Knocks in Chicago.

Eagerly await the Lou Malnati’s x Horween x Ashland butter crust chromexcel collab

Yes, especially when so many people try to find it in china

Stridewise mentioned whale oil as a historical component of CXL, now I’m on a whale oil deep dive. In the Heart of the Sea, Tragedy of the Whaleship Essex by Nathaniel Philbrick has been one of the better books I’ve read in the last few years. Whale oil was banned in 1972, used widely in automotive transmission fluid and margarine before then, some sources describe components that are similar in jojoba and fish oils; when did Horween transition out of using whale oil and to what scale was it used in the past? Apparently the shift caused some major problems way later in history than you’d think: “The trouble involved the cooling unit for the automatic transmission oil, which is placed in the car's radiator. The fittings between the cooling unit and the radiator gave no trouble when whale oil was the fluid, but the substitute allowed the fittings to corrode. That permitted the oil to get into the radiator's cooling system and the radiator's antifreeze to get into the transmission. This damages both the radiator and the transmission, requiring a major overhaul, which normally would cost more than $400. But under an informal arrangement, G.M. says it has been paying for the work no matter what mileage was on the cars. General Motors estimates that its repair bill from the transmission problem will be $2.2million. The company says it will pay for repairs, estimated at $400 a car.” NYT 1975 “In North America alone, 55 million pounds a year sperm whale oil were being consumed. Little did anyone know that the car-driving public was about to learn a painful lesson - their automobiles’ transmissions were in big trouble without sperm whale oil. Thanks to the critical role that sperm whale oil played in making automatic transmission fluids and gear oils, car transmissions routinely lasted for the life of vehicle. Once alternative ingredients had to be found, transmissions began failing at unheard-of rates. Before 1972, less than 1 million transmissions failed each year; without sperm whale oil, transmission failures exploded to more than 8 million by 1975.” University of Washington Magazine, 2019 I left an approximate scale of how many cattle were used to make marine field shoe during WWII in the comments under episode 15. I wonder if we could also get a rough idea of how many whales were needed to produce that much leather.

Thanks again for taking the time to read and answer questions (I know I’ve kind of left a wall of text here), and thanks for continuing to do the world’s best leather podcast

Quoddy still makes Ring Boots as an MTO, picked up a pair earlier this year. I had the expectation that they’d be a little like cxl and tried to wear them sockless, but wound up creating some blood patina bc of the tougher texture. On the one hand they feel like you could throw them at a tank and knock the treads off the tank; on the other hand, they’re breaking in just fine with socks. I can add some context to the questions about overdye and ferrous acetate. They come from what Unsung House has done using homemade walnut dye on engineer boots: kzbin.info/www/bejne/kGLcdYSfd72Bl6Mfeature=shared Grant has mentioned on Stitchdown that he was shooting for a deep even black but wound up with more of a textured brown tone. He mentioned to me trying to use vinegar black, which is common in antiquing gun holsters, and produces black tones by binding iron to tannins (but didn’t work well as an overdye with a finished leather intended for boots). To relate it back to a different question, this is probably more of an application where crust leather would be desired. Through this conversation I wound up reading a manual about dyeing textiles with natural/plant based dyes and I was intrigued by a line in the manual that said that all textiles require tannins to be dyed, except for leather which already has tannins in it. There was also a line about how chrome could be used as a mordant to deepen colors in textiles, but is no longer used in hobby form due to the risk of creating chrome 6. In the antiquing forums they mentioned only being able to use veg tan leathers, and I wasn’t sure why chrome/veg retan leather wouldn’t also work. To bring this back to boots, it’s interesting to see how natural indigo has been used to dye boots as in this oak street boot: kzbin.info/www/bejne/emjKe6Kjna2ha7sfeature=shared I also wound up finding a more stable indigo option through a Japanese tanner/maker called Y’2 Leather (available through standard and strange) which patinas like an interesting cross between denim and leather. They’ve got some cool photos on their website under “About Aging.”

Left out the how the leap to indigo happened. There was a page in the manual about creating near black colors with natural pigments. Indigo plus walnut can create that tone, which also in a way relates to why reverse black shell cordovan is green and tan. Gotta hit that RGB colorway for human eyes to see black.