While looking at unusual garden walls for posts 51 and 53, an even more remarkable wall was noticed at Mount Pleasant Road in Tottenham. Not only are there burnt and fused bricks, beautifully vitrified bricks, there are large blocks of beautifully coloured glass, not just vitrified fireclay, but actual glass! A wall made from glass!
So the question arises, how and why in a set of garden walls probably built between the 1910s and maybe the 1930s, judging from looking at old detailed maps of the area, would the builder have sourced and used these glass blocks for a wall?!  But there is a clue! Again the names of Stourbridge brick makers jumped out: Mobberley and Perry.
So the detective work began and soon, concurrently with discovering gas retorts, it appeared that the same companies also specialised in ‘glass house pots’. And the first thought then is that this referred to a pot for growing plants in, in a glass house. But it is not. A ‘glass-house pot’ is clay-ware that can be exposed to great heat to make glass!
Here is an explanation of their manufacture: “The making of glass house pots varies in manufacture from that of firebricks and gas retorts, in that they are gradually, inch by inch, built up by hand, and that they are not burned, but dried. This process usually takes six month. Messrs. Harris and Pearson are one of the few firms that possess a good mine which yields clay of sufficiently high quality to be suitable for making these pots, and they have obtained the highest reputation for such goods; in addition they sell the clay in the lump state or ground, to other manufacturers. Only a few of the mines in the district produce clay of sufficiently high quality to resist the action of the chemicals inside the pots and the heat outside, and the demand therefore for “Harris and Pearson pot clay,” is very considerable.” 
And again, “Glass house pots were made by one or two works. Their makers were skilled people, but equally so were the men that made gas works retorts. These were much larger than glass house pots, and required as much skill. Weighing in excess of a ton, retorts also had to be man-handled into special kilns, because these vessels could be ten feet in height or over.” 
And ‘glass-house pots’ were indeed made by Mobberley & Perry! 
“There were dozens of brickyards making red and blue bricks in this area who used the seam of clay known as the Oldbury Marl. These bricks were second to none: I am sorry to say that practically all have gone. Mobberley and Perry made red, blue and fireclay bricks and glass retorts, always carrying a large stock of fireclay. Their Hayes Brickworks were on each side of the road at Hayes between Lye and Colley Gate.” From the incredible 1960s “Memoirs of a Black Country Mining Engineer” by Howard Hill 
The “Memoirs of the Geological Survey. Special reports on the mineral resources of Great Britain . Vol. xiv— Refractory materials : Fireclays.” from 1920 states that in fact the Stourbridge fireclay industry was founded specifically for glass making “In this district the fireclay industry appears to have originated in the 1 6th century, in the neighbourhood of Stourbridge, on the south – western borders of the South Staffordshire Coalfield . According to local tradition it was introduced a bout 1556 by some refugee Hungarian glassmakers , who found that the fire clays in the local Coal Measures were such as they needed for their melting-pots.” 
( The fascinating Hungarian connection has been debunked though recently by the English Place Name Society! “… there can be no doubt that this is one of the numerous Hunger or Hungry Hills, so called from the poorness of the soil, cf. Hungerhulle (13thAOMB 61) in Pershore. This one is on the coal measures in contrast to the comparative richness of the keuper sandstone of most of the parish. There is no foundation for the legend that the hill is so called from the glass factory started there by Hungarians.The Henzies or Hensells who founded that industry came from Lorraine.” [6b] )
The 1920 Geological Survey report states of the Mobberley & Perry mines that “The Old Mine Clay, which is black at the top, passes downwards through dark-grey to pale grey. At Hayes Colliery it is more or less black throughout and is especially suitable for making glass house pots and crucibles . At Thorns Colliery the Old Mine Clay is grey and is used as an ingredient in manufacturing glass-house pots”. 
The clay seems to be the same fireclay used for gas retorts going under different names: Fireclay, Refractory, Oldbury Clay, Seatearths, Old Mine Clay, Old Stourbridge Clay, Marls, Muds, Lye Waste etc “The glass house pot-clay is almost peculiar to his neighbourhood. It is inferior to hardly any in Europe, and far superior to any found in England for crucibles, or pots used for melting materials for glass. Indeed it has this property, that a pot made of it will melt almost any thing into glass with proper heat, and provided it be fluxed with proper salts” 
And Lye Waste refers to Lye where Mobberley & Perry were based. “Mud City”, aka Lye Waste. The mud of course was actually Clay, a glutenous, sticky substance, the life-blood of the many Fire Brick Works that sprang up all around the place, and the substance the Glass Works couldn’t do without. Ruffords, Timmis, Fisher, Mobberly and Perry, King Brothers, Hickmans, Harper and Moores, and many smaller concerns, battled for the resources of this tiny area. 
London glass industry
And London had a glass industry as well as Stourbridge’s famous one    and would have imported ‘glass-house pot’s and firebricks from Stourbridge. Terence Paul Smith in the British Brick Society newsletter in 2008 notes that Mobberley and Perry firebricks were found at excavations on old glassworks site at Riverside House at Bankside  also the site of the Falcon Glass Works 
But where specifically, what works, would the glass and the those at Mount Pleasant have then come from? That’s less clear. The Glassmaking in London website documents the industry in London historically  and into the 20thC [ 15] but while there doesn’t appear to be anything local to Tottenham documented there are several classworks not so far north in Lower Edmonton, Ponders End etc.
It’s possible that the builders of these houses had a connection with a glass works and someone simply said “I can get a load of waste blocks from the glassworks. They’ll look great” and the builder got something for free so everyone was happy. And Building London is happy as this is a unique wall and great that they are standing today!
That hopefully explains the glass blocks and firebricks, but what about the brown vitrified bricks? Their colour is reminiscent of brown glazing from the 1920s and 1930s, but why on bricks?
The possibilities include
1) that these are bricks that were being glazed but the glazing went wrong. While glazing was used significantly and mainly for stoneware pipes and ceramic tiles and for architectural terracotta (often called faience in Britain )   it was also used for bricks, often for situations like hospitals, sewers and urinals, in whites and browns, where it can sometimes still be seen. And Doulton of Lambeth,  more famous for their ceramics and sanitaryware also made glazed bricks. 
And worth noting that several glass-house pots makers in Stourbridge also made glazed bricks e.g. the Stourbridge Glazed Brick & Fire Clay Co. Ltd. 
And 2) that these could be kiln bricks in a kiln used for salt glazing. Salt glazing – tends to produce a brown glaze, and again something done by Doulton at Lambeth. Thanks to Chris Wright at Facebook’s Brick of the Day group for this! He also suggests “…fly ash can also produce this effect on the brick surface.”  Also nb it’s mentioned above that salt was used for flux in glass making and maybe that has caused this.
or 3) that these are simply fire bricks from a kiln in a glass-house and that the residue was a result of coal burning. Thanks to Ian Suddaby also from Facebook’s Brick of the Day group for this suggestion.
For now happy to leave this as a mystery but maybe one day someone will work it out, i suspect finding a connection via the builder!