The aircraft of World War I were constructed from wood frame and had high quality linen stretched over it. To seal and protect this linen from the elements it was 'doped' with a cellulitic covering. The dopings used by the British in World War I were commonly known as PC10, PC12 and CDL. Where the PC is believed to have stood for protective coating, and CDL stands for clear doped linen. These were applied over the linen cloth of the wings, fuselage and tail of the aircraft.

The Australian Flying Corps [AFC] aircraft were all from British stock and factories. Consequently the dopings for the AFC aircraft were the same as the Royal Air Force [RAF], Royal Flying Corps [RFC] and Royal Naval Air Service [RNAS]. These dopings were commonly PC10 on the upper surfaces and CDL under the wings and elevators.

PC10 is a bit of a slippery colour for historians to nail down as it changed from a brown to green shade as the war progressed. Additionally as it was subject to weathering it browned in colour.

Another issue is that quality control was not the same in 1916 as it is in modern factories that have the benefits of digital technology and statistical process control. PC10 was very definitely a bucket chemistry proposition.

Bristol Fighter of No.1 Sqn AFC in the protective covering of PC10 doping. The engine cowl is painted in battleship grey.

For one hundred gallons of PC10 the recipe is:

260 pounds nitro Cellulose syrup

74 pounds of pigments in the following proportions:

40 pounds yellow ochre
30 pounds umber
2 pounds 8 ounces Red Ochre
1 pound 8 ounces Chinese Blue

Which was then added to:

20 gallons Acetone or Methyl ethyl ketone
15 gallons Amyl Acetate
15 Gallons benzol
15 gallons Methylated spirit

As can be seen from the 'recipe' it is more like baking a cake than the precision of modern factories which produce identical products 24/7 with minimal variation.

The AFC squadrons in France were very uniform in their dopings; largely being with PC10 upper and CDL lower with either polished or grey cowls. The training squadrons in England had higher variation including red, white and black-and-white checkered aircraft.

The anomaly is No.1 Squadron AFC in the Middle East. They seemed to go through phases where aircraft were relatively uniform in dopings but outside of the standards of the AFC/RFC squadrons in France.

For instance their BE2s and BE12s appear to be uniformly CDL all over until they went through a period where PC12 - PC10s reddish cousin - started appearing on their upper surfaces. The Martinsydes in No.1 squadron went through a similar phase. One aircraft it seems was CDL lower, PC12 upper and a PC10 tailfin - complete with white serial.

Martinsyde G100 of No.1 Sqn AFC with PC12 upper surfaces and PC10 tail. Profile is taken from a photo in One Airman's War

The Martinsydes then appear to have been standardised on all-over CDL before the Bristol Fighter's made their appearance in the squadron. Initially the Bristol Fighters had a mix of white and PC10 markings.

Bristol Fighter A7194 of No.1 Sqn AFC with white and PC10 upper surfaces.

Like the Martinsyde, the Bristol Fighters became standardised in the PC10 uppers and CDL lowers, though one aircraft was recorded as being yellow all over, there has been no photographic evidence of the 'yellow peril' Biff. It may have been ochre, CDL or erroneously reported as yellow.