When deciding what leather to use notice the following:
thickness? (sometimes thickness may be adjusted by gluing thin leather to tagboard, chip board or paper)
shiny or varnished on one side?
rough suede? fine smooth suede? how soft?
how porous? Bubble jar testing is recommended Or see tester below
spongy? stiff or flexible?
alum or chemical tanned? vegetable tanned? chromium tanned? How do you know about the tanning technique used?
Alum Tanned leather is bright white or ivory. Vegetable tanned leather is earth tones or dyed one side. Chrome tanned leather is white with a grey or blue cast to it. Any of these may be found dyed any color if they are not from organ or player supply sources.
TESTING THE LEATHER: Shave off a tiny sliver of the leather in question--about the size of a quarter inch piece of a toothpick. Hold the end of this sliver in the jaws of metal tweezers or needle nose pliers. With a lighter or a long wooden match, hold the sliver in the flame for about a minute or until the whole piece glows red. Then remove the flame and hold the glowing ash still and allow it to cool. When it is cool, it will be one of three colors: if it is white, you know it is chemical or alum tanned leather, if it is black, it is vegetable tanned leather, if it is blue or blue/green/gray, it is chromium tanned.
Use a strap Cutter (for cutting Belts) to cut gasket strips that need to have straight parallel sides. If the leather you use has a slick varnished side, and you need to glue to that side, you must first sand off the varnish or no glue will stick well. You might consider sanding before cutting as sanding may sometimes stretch the leather. This is especially true if you must punch a row of holes in a strap of leather. If you need to sand cut straps, use the rounded end of the belt sander belt with the sander running and keep the strap moving from end to end.
When cutting pneumatic leather (thin pouch leather) watch out for pinholes at the armpits of the skin. Some suppliers will mark the holes with felt pen. To cut thin pneumatic leather a strap cutter will not work. Use two thin aluminum or other metal straight edges and lay the first one on the line to be cut. Then lay the other one on the other side of the line. Firmly press them down and using a sharp razor blade, slice down between the two straight edges.
When cutting a skin of pneumatic leather start with a cut lengthwise right down the middle. This will give you a straight line to start your cuts with. After the next cut or the next one you may be required to cut out a wedge between strips in order for the leather to lay flat. Always use SHARP razor blades to cut leather so you will have a straight clean edge. When the blade is dull it chews instead of cutting and it may look like its been cut with pinking shears.
You may also cut pneumatic leather with a rotary cutter of the type used to cut out quilting fabric. A cutting pad is needed to use the rotary cutter. The cloth store sells such a pad, but it is not as good as what is available from the die cutters supply. The red die cutting pad is the best one. They sell a white pad for cutting woven cloths. The black pad sold at Tandy for shoe soling is good but is quite soft and the red one is better for our purposes.
Here are pics of a leather tester that I can take with me to the leather warehouse.
They think I am crazy when I do this but I found the best leather I had seen for years. This is one of the reservoirs from a standard bellows that sometimes you must remove to install the suction box. It is recovered with the inside boards well sealed with shellac.
The red pouch and dark khaki valve leathers that I use and sell are the best leathers I have found for some years. The Khaki kid skin takes about 6 minutes to open the bellows. It is the same time as when I cover the hole with masking tape. The other leathers I tested took between 1 and 2 minutes to open.
Pictures coming soon
Doug L. Bullock, copyright 2000-2009