Up until about a year ago I could soften any hide that came my way. Then I met a ~15 sq. ft. buck hide, and I softened it....4 times, to no avail. Multiple eggings and wringings and all that.
So then I met a guy named Mark Humpal who taught me about pre-wringing with a detergent soap (I use fels naptha) to break down the hide glues, especially in those thick hides. And then egging/braining.
So I've been okay MOSTLY, except when I tan certain hides. I get hides that have been caped (had the top half taken off) for taxidermy. And some of these hides were so big originally, that just the haunches look to be the size of an average deer hide. I just tried tanning one of these, with the pre-soaping technique, and it came out stiff along the back and haunches. I haven't learned bucking/acidifying yet, so I'm working on learning that, but other than that, is there some trick to getting these thick hides soft? Also...I soften on a rack and then cable afterwards, which gets me out of most stiffness situations, but this hide just plain won't soften, even with aggressive cabling.