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Old 04-04-2005, 04:42 PM
Durk Valkema
Posts: n/a

In the Netherlands in the 60th there was a scene of artists using flat glass from England Germany or France, fusing colours together, adding potash between sheets for volcano effects and at the end holding it all together with the newly developed acrylic and epoxy based glues. Things cracked and empirical experience was developed, hot forming was done in bell type kilns with big open gas flames, very uncontrolled annealing but in the end it was all glued together. Until after 20 years the glue falls apart.
Rods in the blown glass scene where used by factory's well before we where born and with enough knowledge to do the ring test and adjust or even the tests measured on the polarimeter according to the Philips method.
I know Orrefors used to make Kugler hold a melt, get a sample to test on the polarimeter and if it was close enough buy the whole melt.
We at the academy in the 70th, where stuck with cullet from the automated gobbletery at Leerdam, new which colours fit. The cullet was our constant and we knew about the ring and cane tests. Now non of the students have a clue.
Some studio people in the 70th batched themselves but all with links to helpful engineers in the glass industry.
Otherwise it was Harvey's Glassblowing with Erwin's recipes and Frank Kulasiewicz book apart from Sholes and Weyl.
My father started to hand out photocopies of the fascinating "receptbuch fur die praktische Glasschmelzer" by Schmidt to all the interested visitors, I used the book in the early 70th to melt colours at the academy in the colour pot furnace we build knowing vaguely about expansion and ways to make things fit together. Got a hold of S. Simmingskold Ravaror for glassmaltning (Published in 1963) in 1973 while I was at Orrefors. With an add for Polarizing microscopes but no mention of expansions.
Later on in the 70th we got a copy of internal educational material from Philips with very detailed and up to date information on the chemical and physical properties of glass.
Still we used the cullet available to the academy for free.
Pelletised batch came into the picture much later. In the early 80th I did extensive tests for Rhone-Poulenc with their "CRISVER route" material developed by Mr. Richard. An alkaline silicate was made to react with metallic nitrates in water or an organic solvent. The result is a precipitate of organic oxides and by product alkaline nitrate, which is filtered off. During synthesis, these oxides take up the same arrangement, as they will have in the vitreous state. Consequently, such melts vitrify faster and at lower temperatures than traditional compositions. Or so it seemed. One way to try find new markets for their water glass.
Philips started to develop a plant for palletizing there base of hundreds of special glasses that they would melt only a few times a year in there glass factory " Philips Lighting" build in 1980 in Winschoten.
It was not until 10 years later that they started to make there batching facility available to outsiders and market a few basic batches available like a 24% PbO glass with in the tech. info viscosity info and average expansion coefficients:
25-300: 9.35
25-400: 9,65
And an annealing curve.
For the "studio glass" scene they developed a lead-free batch Nr 2500
They knew we used colour rods in our pieces, but the only source they knew about was the Murano cane so the average expansion coefficients at 10,10 (25-300) and 10,55 (25-400)
You can imagine that suddenly a whole different range of colours exploded.
The 2400 worked much better but who wants 2% lead out the chimney every melt.
It took a lot of time to convince them to steer the lead free more towards the German rods.
In the mean time GLASMA was started and again after initially producing exclusively for the factory's they started marketing a lead free pelletised batch.
We knew about Spruce-Pine but that was expensive and far away. Lots of sources for cullet in those days.
Still everybody experimented and knew what to expect most of the time. If it survives the diamant saw its OK.
Very low tech.
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