RW Hopkins

…started his slag project at the Owens Illinois plant at Charleston, W.Va. with blast furnace slag he had obtained at a slag plant in Pittsburgh, Pa. He had asked the company to make the slag sizing from about 16 mesh down in size to whatever resulted from using a 16 mesh top size screen. Generally speaking, the amount passing 100 mesh resulted in about 25 percent of the product which seemed to be not too fine. The object was to make a product sized reasonably close to the other raw materials being used in order NOT to have “selective” melting.

In addition, he asked the slag company to run the material over some “Head” or “Drum” magnets to remove the excess iron, especially shot (bee bees) which if not melted would come out as defects in the bottles. RW had a difficult time with the slag he received and 01 lost a great deal of production during the time that he was working on the slag project. Finally after several years of off and on projects with slag, things started to settle down and slag, which was initially used ONLY because it was a cheap source of ALUMINA, proved to RWH that it had other rather remarkable characteristics.

Better Glass Production

RWH during his time as a batch and furnace man with little instrumentation to go on, had to use his imagination and intuition in melting glass. He knew better than most engineers how the furnace melted the normal raw materials and noticed that when slag was employed the glass melted faster and he could make a more stable amber thus being able to increase production of a better quality glass most of the time. There were other problems, however, which proved to be puzzling. He discovered that by altering the quantities of slag he could effect both the color and quality. He solved some of these problems by adding iron and also sulfates usually in the form of salt cake. Balancing the quantities of slag, salt cake and iron proved to be both a difficult and perplexing problem but he was determined to solve slag employment in amber glass.

Ignorance almost ruined Slag

Things were going along fairly well at t he Charleston plant when all of the sudden the bottles were being produced with shot pieces in the glass. Owens Illinois was losing approximately 95% of their amber production. Needless to say, the plant executives and Toledo were going crazy and demanded that slag be removed immediately. After removing the slag, RW Hopkins went immediately to Pittsburgh only to discover that the slag company had removed the magnet for some repair work and neglected to tell anyone. This one incident almost destroyed the slag concept in the United States.

As a result of the undependability of a slag company without glass knowledge and experience to manufacture a dependable product; RWH decided that if slag was going to be a viable product, someone who knew glassmaking was going to have to be involved in the slag manufacturing process.


In 1944 RW Hopkins made a deal, first, with Owens Illinois that he would see that the product was made correctly if they would keep him on the payroll while he got a small company started that would oversee the manufacturing of the product and then help with the implementation of its use. He, secondly, made a deal with a slag and gravel company, American Materials Inc of Greenville, Ohio, to produce a slag product at their Hamilton, Ohio plant (Armco Steel) to glass specifications (ones that he had set while at Ol) for a certain price which he intended to add a dollar for his expenses. He called this new company “THE CALUMITE COMPANY”- Calumite being a contraction for CAlcium, ALUMina, and SilicaTE the three main ingredients in slag. The first sale to 01, Charleston, was in August 1944 and was a total of 22 tons. He grossed $22 dollars that month.

In time, the business started growing (the product was priced at $3.50 per ton) and in 1948 another Calumite Operation was started at the slag plant of the Illinois Slagand Ballast Co in South Chicago (Wisconsin Steel). In 1953 a new water quenched product was produced at Middletown, Ohio (Armco, now AKSteel) by American Materials and with the very low sulphur in the material Owens Corning Fiberglass in Newark, Ohio contracted for 50,000 tons per year at about $4.00/ton. A new and first time stand alone plant was constructed which was then the state of the art. Up until now all the Calumite tonnage was made alongside other slag products in a basic slag plant. The crushers used for the Calumite product were Eagle hammer mills, type IR separators (iron removal), and Midwest screens. The material was dried, crushed (mostly pulverized unfortunately) and taken by elevator to the top of the plant and then put through screens, magnetic separation and stored in silos.

The next plant site was Morrisville, Pa with the Warner Company (US Steel) and then came Granite City, IL (Granite City Steel) with St Louis Slag. This plant was built with some strange ideas from the President of St Louis Slag, Doug Street, and was doomed from the start with its Aero Separator with no screens employed. This Aero separator was supposed to lift the sized material and let the coarser slag drop back into the crusher. Unfortunately, Doug Street never took into account that slag particles have different densities and the same size could rise to different heights in the Aero Separator. This plant was built about the time the steel industry was adding VERY refractory materials in the slag runners to cut erosion and reduce their labor costs. The Granite City Calumite plant ended up shipping some course slag which did not cause the problem, in our opinion, but poor engineering on the part of the glass company and poor consultants (who were competitors at the time of one of our companies) to the glass company who blamed our Calumite product for their glass problems. A law suite followed and soon thereafter the Calumite plant at Granite City was shut down.
The Calumite Company moved their offices to Morrisville, Pa in 1962 at the time the new eastern plant was opened and a few years later moved across the Delaware River in the vicinity of Trenton NJ to a large specifically designed office and laboratory building adjacent to the 1-95 motorway.

One more small plant followed at Weirton, W.Va. (Weirton Steel) with Koch Industries. This slag was a true granulated slag that was used by Koch for a cement product with a left over size going to make a Calumite product.


The chemistry of air cooled slag is basically the same or very similar no matter where in the world it is found. But through the early days in Hamilton, RWH started concentrating on how to stabilize the amber glass which was difficult because of the great variations in the slag from day to day. RWH concentrated on developing the initial ReductionOxidation (REDOX) theories that he had thought about for years. He considered the tank of glass as one big chemical reaction that had to come to a state of equilibrium. If he was correct, and time has proven this to be true, then we should be able to assign numbers (oxidation or reduction) to each material and work out a balance before introducing the mixed batch into the furnace.

Today, every glass man in the world uses the REDOX system that RW Hopkins pioneered in the 1950′s. He also developed the theory many years before the industry accepted that glass flowed a certain way in the furnace and could be altered by introducing certain materials and by adjusting furnace temperatures. An understanding of these two theories, REDOX and Flow in a Glass Tank is imperative to the successful employment of Calumite slag.

Owens Illinois started using our Calumite product also in oxidized flint glass to purge the sulfate (503 to 502 gas) which came out of the glass and which allowed the glass companies to pull MORE clear, un-seedy glass out of the tank.

In Trenton our phone started ringing from England, Europe and Japan. From this we formed joint ventures. Calumite Limited, CAL5A and Nippon Calumite were formed in the 1960′s and 1970′s. Later, Calumite SRO and Calumite Iberica were started.