Volume 10 - Autumn 2000


The Manufacture of Leather - part 10

by Roger Barlee

In Part 9 of our series "The Manufacture of Leather", I described the processes involved in the finishing of our bookbinding leathers. I finished the article with the leathers leaving the finishing department on route to the warehouse, and in this article I am intending to give a little insight into the workings of our warehouse including a discussion on our system of grading leathers.

Measuring Skins

The Pinwheel Measuring Machine

In many tanneries, leather is now measured using light scanners fitted to the conveyor belts in the finishing department. The official method however, and the one that we use, involves the use of a pinwheel measuring machine. This wonderful contraption is made up of a series of metal wheels, each of which has a series of pins, one inch apart, protruding from its circumference. The wheels are positioned so the pins on adjacent wheels are also one inch apart, and these pins pass through grooves on the bottom roller when no skin is present. When a skin is passed through the machine, the pins that come into contact with the skins are pushed up inside the wheels, turning a cog that is connected to a dial through a series of further cogs and wires.

The Pinwheel Measuring Machine Schematic showing the workings of the Pinwheel Measuring Machine  Although many of you will have encountered "square metres" before, a few of your newer customers will be wondering what has happened to the much loved and still lamented "square foot". A number of years ago the European parliament ruled that imperial measurements were to be phased out and replaced with their metric equivalent, and we were reluctantly forced to go metric. You may be surprised that our 1950's British-made measuring machine was already dual marked and did not need to be converted! As a guide I have listed the conversion factors below.

8 sq.ft.= 0.86 sq.m. (multiply by 0.929 or divide by 10.764)

£6.00/ sq.ft. = £64.58/ sq.m. (multiply by 10.764 or divide by 0.929)


Schematic showing the workings of The Pinwheel Measuring Machine


Please remember all the current staff were brought up on the square foot, and are quite willing to accept orders in square feet and convert for you.


I write about grading with a little trepidation. The reason for this is that everybody has their own ideas about how a skin should be graded. I thought however that it would be worth putting J. Hewit & Sons grading system down on paper considering that we are now dealing directly with more new customers since the advent of our on-line web catalogue. I am going to divide the leather types into "Commercial" (all resin pigmented leathers) and "Craft" (all leathers suitable for handwork).


I have included in the commercial leathers all smooth, glazed and embossed pigmented leathers. These leathers are generally only sold in 2 grades, 1st and 2nd. Generally the grade I skins are blemish-free, although it is possible that a small defect might be found at the edge of the skin. Grade 2 skins will have either a hole or some defect that has not covered with the embossing or haircell print, however in most cases there is still sufficient clean area for at least one full binding. As a rule we normally assume the glazed sheep skivers are more often going to be used for titling pieces, and this results in a higher proportion of grade 2 skins being found in this leather.

Craft Leathers

I have included in the craft leathers all those leathers with a natural grain suitable for handwork - Bookcalf, Chieftain and Clansman Goats etc. The majority of our craft leathers are available three grades - 1st, 2nd and 3rd.

I am first of all going to mention Bookcalf, (and associated pure aniline leathers). In the case of these leathers where there is no surface coating at all the number of perfect skins runs at only about 1-2%, although there is a sizeable proportion of skins with VERY minor damage. In the case of Calfskins this small percentage are separated out as "Super" grade, whilst the "near perfect" skins are sold as grade 1. Don't expect to be able to order 15 Super quality calf at one go, but if you require one or two perfect skins for some priceless book they are there if required.

With the other craft leathers where there is a degree of surface coating, the 1st grade skins, as one would expect, are as a whole blemish free. There might be a small defect on the belly edge or up in the neck area of the skin, but any such damage should be outside the main cutting area in the centre of the skin. Whilst it would be wonderful to be able to offer all grade 1 skins, we do not live in a perfect world. The proportion of grade 1 skins varies depending on the leather type, but is normally in the range of 10-25%. The bulk of what is left is made up of grade 2 skins.

All grade 2 leathers have some sort of blemish on the grain or flesh of the skin that will show up if incorporated into a binding. These blemishes can vary from a flay mark on the back of the skin, through scratches to holes in the skin. As a rule grade 2 skins will have sufficient clean areas to allow at least one full A4 binding to be cut blemish-free. On the smaller leathers such as the Clansman Niger this is not always possible, and in these cases a view is taken on whether the blemishes are "closed" - can be incorporated into a binding, or "open". There has, of course, got to be some sort of boundary between a grade 2 skin and that of a grade 3 skin, and this by its very nature has to be indistinct. The grading will depend on the number and severity of the blemishes taken in relationship to the size of the skin. A large skin with several major blemishes concentrated in one area leaving a good clean area on the skin will be classified as grade 2, whilst a smaller skin with a series of minor marks scattered over the whole surface will be downgraded to a 3rd grade skin.

This system of grading has worked fairly successfully for many years with our customers in the UK (although I'll no doubt now be flooded with complaints!!). If you are at all unsure of the grade you require, or have an unusual book size, it is worth noting that we are very willing to size skins to customer's requirements. This generally benefits both J. Hewit & Sons and you as Binders since you will receive the most price-efficient skins available from stock, and we can hold onto the limited numbers of grade 1 skins for those customers where price is of lesser importance.

Cutting Service

The last service that we provide is our "post production" operations. To date the only service we offer is our cutting service, however we are contemplating offering limited foil blocking and machine paring in the future.

Many of you will have little use for our cutting service, however if you are involved in the production of large quantities of books of the same size this may be of interest. A few years ago J. Hewit & Sons purchased a clicker press used for producing cut pieces, and have been offering this service out to some of the larger commercial binderies. We offer this service at cost price, with the Binder having to pay for the knife, the labour and running costs of the press. The cost of the cutting works out at around 11 pence (0.11 GBP) per piece plus the price of the knife (20-60 GBP). As a general rule hand cutting is more cost efficient up to around 300 pieces, the larger the job the more efficient machine cutting becomes. If you are interested in a quotation for any up and coming project please let us know.


Skin Deep - Volume 10 - Autumn 2000

Download Skin Deep - Volume 10 in PDF Format