The best all round leather is organic tanned calf skin with a thickness of about 1.5mm. Also usable is 2mm panel hide. This tends to be stiffer and more porous but, with careful selection and a good sealant, will be usable ( I have made a number of successful bags from this). If in doubt about the porosity of the leather hold a piece to your mouth and suck air through it. It will allow some air through but should need a good "suck" to do so.
Chemical (chrome) tanned leather is more readily available and in general is cheaper. (To check if the leather is "chrome tanned" look at the edge, if it has a central strata of a greyish white colour it is likely to be). These leathers can be used despite the historical recommendations to the contrary.
Example of a bag freshly sewn.
Example of a glued Gortex bag.
The shape of the bag is a matter of personal preference but I do prefer the shape given here. This is very close to the shape used by David Burghley and feels very comfortable under the arm. From a design point of view it is important that the drone stock is positioned not lower than one diameter down from the top of the bag and far enough forward to place the chanter in a comfortable position. The blowpipe stock should be as low as possible (leaving room for the tieing in) and vertically below the drone stock.
Cutting to shape
Cut a "half bag template from stiff cardboard or thin ply, mark the drone and blowpipe stock positions and cut a circle 2mm smaller than the diameter of the stock. Lay out the leather on the floor with the inside uppermost, inspect very carefully for damage or thin areas (mark any found with chalk or biro), lay the template on the leather moving around until the full shape avoids all imperfections, mark a centre line on the leather to line the template up with, cut round using a very sharp knife, turn the template over and cut the round the other side. The shape should be again checked for any faults ( if any are found a piece of leather can be glued on the inside ). Mark the stock positions from the template taking care to produce a "right hand bag" and cut a series of diametral cuts across the centre like this.
The bag can now be glued. Prepare an area about 10mm wide around the edge of the inside surface by smearing a thin layer of "UHU" glue, allowing to dry, recoating with more glue and pressing together taking care not to allow the area glued to exceed about 10mm width. From the scrap leather cut a strip about 40mm wide and as long as the sewn edge of the bag ,this is glued around the edge, using a similar technique. Picture of the glued strip here
Sewing the leather
The leather is sewn with a strong well waxed hemp thread using a "saddle stitch" through holes punched using a "awl". The holes are spaced approximately 5mm apart and about 5mm in from the edge and go through all four thicknesses of the leather. start at the end furthest from the neck, pass one end of the thread through the first hole and pull about 300mm through, take the other end of the thread and pass it through the same hole from the other side. Pull the thread tight so that there is the same amount of thread out of each hole. Pass the first end of the thread through the second hole from the same side as it emerges and the second end through the second hole from its side. The threads are again pulled tight. This is repeated all the way round the edge finishing by tying the ends over the neck end. The thread will follow a figure of eight path with each end crossing over in a hole.
When the sewing is complete the overlapping strip can be cut back, leaving about 5mm inside the line of stitching.
Tieing in the stocks
The stocks are held in position in the bag by binding the leather to the stock with strong cord. My favourite cord is "STUR-D-LACE" braided dacron lacing tape with a breaking strain of around 50lb . This normally used to lace electrical cable forms in aircraft and other industrial applications (used by NASA for tying cable forms in the shuttle). You may be able to obtain it or a similar material from an electrical firm. If not you should use the thinnest cord that cannot be broken with a sharp pull. You will be pulling the binding very tight and it is very frustrating if the cord breaks and the wrapping has to be restarted from scratch. The cord must be well waxed by pulling over a block of bee's wax to help it grip firmly.
Start with the blowpipe stock, put it inside the bag through the drone stock hole and bring it out through it's own hole pulling it out until the groove in the stock is just inside the leather. Take a length of the cord and anchor one end and wrap one turn round the leather just above the groove and pull tight continue wrapping round the leather pulling the cord as tight as possible until the leather is firmly held ( usually about 10-15 turns ) and tie the ends of the cord together firmly.
The drone stock is pushed through its own hole small end first until it is entirely inside the bag, turn it round and bring it out through it hole until the groove in the stock is just inside the leather as for the blowpipe stock. Before binding to the bag the stock should be rotated until the smallest drones are facing the neck end of the bag and the largest drones are at the back. Bind to the bag in the same way as the bellows stock.
The chanter stock requires a different method of tieing in to cope with the seam of the bag. A piece of leather (bag offcut) 20mm long by 10mm wide is rolled into a tube about 4mm diameter and a few turns of thin thread wrapped round to hold it to shape. The stock is pushed into the neck of the bag until it is about 20mm (3/4") in. Hold the neck in the left hand with the stock pointing to the right and the bag seam pointing towards you, fold the seam upwards round the stock. This will fit the leather of the neck closely to the stock except for a small gap under where the seam is folded, take the piece of rolled leather and place it over the gap holding in place with the thumb of the left hand. Take the cord in the right hand ( the cord is anchored at one end as before ) and bring it under the stock and wrap it round the leather pulling as tight as possible. The rolled piece of leather will be pulled against the gap closing it. Continue wrapping round until the stock is firmly held and tie the ends of the cord as before.
The bag should now be checked for leaks. Plug the drone and blowpipe stocks with corks, blow up the bag through the chanter stock, put a cork in this stock and hold the bag close to the face whilst pressing the sides of the bag firmly. A general, gentle loss of air through the leather is acceptable but if any leaks are found in the stock/bag joints they should be rebound as is is easier to do this now than after the bag has been filled with sealant.
Sealing the leather
The sealant used to seal the Northumbrian small pipes is different from most other bag pipes because the air used is pumped from bellows rather than mouth blown. This means that the sealant does not have to absorb moisture nor protect the bag from rotting caused by water. None of the proprietary bag sealants can be recommended, indeed they should be completely rejected as more likely to cause problems than cure them!
The mixture I use to seal the leather is as follows:-
25gm (1oz) of beeswax
25gm (1oz) of colophony resin (fiddle bow rosin)
25gm (1oz) of white petroleum jelly (Vaseline)
250ml (1/2 pint) neetsfoot oil
Melt the beeswax, the rosin and the Vaseline together in an old saucepan taking extreme care as all of these materials are inflammable. When they are well melted and mixed together pour in the neetsfoot oil and continue heating and stirring until all of the constituents are blended together and at a temperature hot enough to flow well but not scalding hot ( about comfortable drinking temperature! ).
Remove the cork from the chanter stock and pour about half the mixture ( about a cupful ) into the bag whilst holding the drone stock up to avoid allowing any of the sealant into it, recork the chanter stock and swill the mixture all around the inside of the bag. You will need to be fairly quick as the mixture cools quite quickly. Rub the sides of the bag together firmly to work the mixture into all the nooks and crannies ensuring that no area is left uncoated. Remove the chanter cork and blow some air into the bag, replace the cork and press the sides of the bag firmly to force the sealant into all of the pores. At this stage it will become apparent whether the sewing, tying and sealing have been successful. If any problems are found they must be tackled at this stage to avoid problems later. A general slight leak is often caused by insufficient sealant reaching some areas of the bag and can be cured by adding a little more and rubbing in well. Do take care however not to have excess sealant in the bag as lumps can break free and get on the reeds causing damage. Pouring in sealant will not cure poor stitching nor slack or inadequate binding of the stocks.
Further notes on the bag
If the leather is of very fine quality it may need no sealant added to seal. I have found that good calf with a smooth inside surface can often be completely air tight and if the stitching and binding is well done the bag will need no oiling at all.
Some makers use neetsfoot oil on it's own to seal the bag, pouring an excess of oil in to the bag and, after working it well into the leather, hanging the bag up and allowing the excess to drain out of the neck.
I have also seen successful bags made from rubberized canvas glued together, requiring no sealing at all.
After a bag is sealed I put it in a cover made from toweling to absorb any excess oil which may soak through the leather, so that when the set is complete it can be assembled into its final cover without the risk of oil stains.
Take care to remove any sealant which may have got into the stocks. This can be done with a piece of cloth wrapped round a stick.
drawings to be added (and more information) as soon as I have time