It took three more months of investigation to establish that the original un-flawed glass had been produced through a ‘fluke’ occurrence, and that the real secret of a perfect surface was the relative temperatures between tin and glass and the rate of cooling before rolling and annealing. The glass ‘floated’ because it was of lower density than the liquid metal, but time was needed to allow glass surface irregularities to ‘flow out’ across the dead flat surface of the molten tin. 

 

Problems remained, regardless of the incoming thickness of glass, physical characteristics dictated that 4mm was the ‘natural’ thickness of the final sheet. Fortunately, this was in no way a disadvantage since this was a preferred width for glazing glass.  Later development (toothed rollers to increase flow speed) overcame this and made possible sheet glass in a wide range of thicknesses. It is interesting that Pilkington later confirmed that had he been aware of previous unsuccessful efforts to perfect the same technology he might never have tried his method. Two Americans, W.R.Heal in 1902, and H.K. Hitchcock in 1905, had patented very similar methods but, as the U.S Patent office ruled, had not successfully produced an ‘operative process’. Pilkington Brothers spent some £7,000,000 perfecting their process but ultimately reaped enormous profits from licensing the process in 12 countries to some 22 manufacturers. Coloured float glass was subsequently developed, as too the now famous ‘K-Glass; made by depositing a copper metallic coating laid on thinly enough to be transparent to visible light, but tending to reflect heat. 

 

Lionel Pilkington was knighted in 1970 and became chairman of Pilkington in 1973. Intriguingly, Lionel Pilkington was only remotely connected with the Pilkington family which owned Pilkington Brothers.