Whilst thanking George Formby for the title of this piece, I’m sure unlike DAS volunteers he had never cleaned and polished around 90 VC10 cabin windows! This onerous task had fallen mainly to the Tuesday team and it was one of their members Dave Coates who was bemused about why all the windows had vertical stripes in the Perspex.
After some head scratching it was thought this was due to masking tape being applied to the windows during the last fuselage repaint. Dave wanted to find out more so took an old window along to a friend of his who is an expert on Perspex/plastics for his comments. What follows is the result of his enquiry. Our thanks to Dave Coates for finding out exactly what has caused the damage.
Damage to VC10 window - report
The striations on the sample damaged window are regularly two inches apart. This indicates that, as Dave Swann (DAS Engineer) suggested, the windows may have been masked during the re-painting of the aircraft. two-inch masking tape being a regular masking purchase of old. It is also noticeable that the edge of the window shows more damage that the internal surface.
The paint used for aircraft in the early to mid-60s would invariably have been solvent base, a cellulose nitrate (nitrocellulose) or an alkyd or even an epoxy formulation. If for the re-painting of the aircraft during its life as part of the British Airliner Collection, or even pre-Duxford days, a similar paint was used there is a high probability that the masking of the windows allowed migration of solvent (through seepage or capillary action) to the perspex (PMMA) window material.
It is well documented that PMMA is dramatically affected by solvent materials (either by dissolution or softening). I won't go into the technical details but (museum) conservationists at Glasgow University have been studying the effect of solvent material on PMMA artefacts for many years.
The solvent could have been any of the common industrial solvents, acetone, ethyl acetate or similar ketone or ester-based materials.
We have noted that the windows on the South East side of the plane (port-side) are more damaged than those on the North West side and this could be the result of longer exposure to UV degradation.
Attached is a collection of 200 times magnification photographs of the window (Fig 1) showing the type of failure. These photos support the notion that the damage is caused by solvent penetration.
Fig 2a. Shows damage formed along the capillary gap between two pieces of PTFE tape (removed) when a new piece of PMMA was exposed to pure acetic acid for 2h. In this case Acetic acid can be regarded as a polar organic solvent rather than an acid (This is not likely to be found in paint but happened to be to hand)
Fig 2b. Shows the surface of a piece of new PMMA exposed for 30 min to organic solvent THF. THF is a widely used solvent (including for paints).
As a result of this exploration, I would like, if possible, to check when the VC10 was re-painted and whether the windows were masked with 2-inch masking tape.
I am not sure where this is leading but one thought is that this might help in dealing with other PMMA/plastic components to be found in the collection (both DAS and IWM?).
Thanks to Dave and his friend for this detailed investigation as to what the vertical lines were. As a matter of interest the VC10 cabin roof was repainted back in 2016 but I do know stripper was not used the old paint was just rubbed down. However it may have then been wiped over with panel wipe which could have run down onto the windows but again I can’t remember if they had been masked or not. I have no recollection as to when the cheat line was last repainted.
Thanks again to Dave Coates for providing the information for this unusual article.