It is hard to put your finger on precisely what makes really good leatherwork. Frankly I'm unable to define it but I've tried to put down a few of my thoughts below. I've concentrated on cowhide as that is what I tend to work with, but I believe the principles apply to all types of leatherworking.
Is it just the quality of the leather? I don't believe so as I've seen some truly horrible bits of leatherwork made from utterly gorgeous leather. Certainly, leather quality plays a part, but I believe good leatherworking is a combination of both materials, craftsmanship, functionality, aesthetics and an utterly indefineable 'WOW' factor. If you smile, get goosebumps or even want to shout out loud when you see a fabulous piece of leatherwork then you know exactly what I mean.
Materials first: we need to recognise from the outset that leather is a manufactured product. It isn't just the skin of an animal. The average cow skin arrives at the tannery on a pallet; 'wet' and fresh from the slaughterhouse. It still has hair on it and is covered in fat and detritus from the slaughterhouse floor, it is not leather. This is the tanner's raw material. It is a small miracle that the frankly revolting wet skin can be de-haired, treated, plated or pressed to make it smooth and turned into beautiful leather.
The care the tanner puts into the tanning process adds enormously to the quality of the leather and subsequently to the finished products that are made from it. It is understandable that some tanners are a tad 'precious' with their product and favour established craftspeople.
The tanned hide arrives at the craftsperson's workshop, pristine and unblemished - only that simply isn't true!
Every hide comes complete with blemishes, scars, scratches, cuts and obscure flaying knife damage. It has to be assessed with an expert eye to ensure the right sections are turned into the correct products. It has to be checked by eye but also by hand. You will see the leatherworker running their hands over a hide prior to cutting, checking for soft patches, imperfections and almost invisible damage.
The skill required to cut leather efficiently and in a cost effective way is enormous and only learned by experience but knife sharpening, stropping, pattern making, finishing and fitting accessories are just a few of the skills required to produce acceptable leatherwork. True 'quality' leatherwork requires an even higher level of commitment from both the craftsperson and the tanner and includes the fittings manufacturer, the thread maker and the colourist who dyes the hides. Leatherwork is rarely the product of a single person.
The choice of fittings has to play a part in quality leatherworking. Cheap shoddy fittings are never acceptable but good quality is hard to find. Most of the traditional British manufacturers have now closed their doors so the leatherworker generally needs to hunt further afield. Italy is my personal favourite but I've seen excellent leather fittings made in India, China and Taiwan.
Having cut the leather to shape, the work needs to be stitched/riveted/glued ready for finishing and final assembly. Hand stitching has always been seen as the ultimate mark of a quality item, but the latest sewing machines come a very close second these days. Stitching through 7-8mm of leather takes a degree of skill, strength and confidence that takes years to perfect.
Hand dyeing leather to bring out the grain and character of individual pieces is a highly skillled job. Honestly, it is too complex to describe the process other than to say it isn't just wiping dye onto the leather with a rag. The dyer must be able to recognise the characteristics of each piece they work on, understand where on the animal the leather came from and reflect that knowledge in the way they apply the dye. It isn't surprising that many leatherworkers like to work on tannery (drum) dyed leather with its bland but consistently and evenly coloured surface. Does working with drum dyed leather actually produce top quality work? You can make up your own mind...
Finally, leatherworking generally combines aesthetics with a functional requirement. If a piece of work fails the aesthetic test but functions perfectly it might pass muster, but if it looks beautiful but fails to work then it goes in the scrap box. Ouch!