This is the history of a Shore hardness tester that was purchased by Viskafors Gummifabrik in the mid-forties.

In 1986 the Swedish Rubber association (SGF), organized the first International Rubber Conference (IRC) held in Sweden. At that time, I worked at the Swedish National Testing Institute (SP) and we participated in the exhibition.

Our Polymer laboratory had organized one of the first Interlaboratory test programs (ITP) for ISO TC 45, Rubber and Rubber products. The ITP was for Shore and IRHD hardness and 52 laboratories around the world participated.

We organized a competition in our both at the IRC exhibition with the 4 rubber materials from this ITP. We attached the rubber samples in Petri dishes, so you only could estimate the hardness value by pressing your thumb on the samples.

The competition became very popular and a lot of visitors participated. After the exhibition we had two winners, both were only one hardness degree off on one of the samples, compared to the mean value from our 52 laboratories. Compared to the spread in the results from the laboratories with 7,3 Shore A degrees. One of the winners came from the Netherlands and the other from Sweden. It was Per Normelli, the secretary of the Swedish rubber standards committee.

Later at an SGF meeting we gave Per a price and asked him how he could be so good in estimating the rubber hardness by his thumb. Per told us that when he worked at Viskafors Gummifabrik, in the mid-forties the technical manager Christer Nordensköld purchased one (only) Shore A hardness tester and the personnel then had to train to estimate the hardness with their thumbs by comparing with the Shore tester. This training was so good that even after 30 years since Per had worked in a rubber factory, he still could “measure” the hardness by hand.

The Viskafors factory was closed 1990 after 100 years and was then owned by Trelleborg AB, I had myself started Elastocon AB 1989 and I got the possibility to purchase some laboratory items after that other Trelleborg companies had collected what they could use. I purchased laboratory glassware, an oven, a TR-tester and an old Shore A tester.

The Shore A tester is marked STANDARD on the back and in the box was a note written by the laboratory manager Olle Carlsson 1955, saying that this instrument may only be used to compare other hardness testers. This must be the tester bought in the mid-forties.

I had worked at Firestone-Viskafors between 1966 to 1978 and used this tester for “calibration” once a year. In between it was locked into the laboratory safe.

Now I have the Shore tester in the Elastocon museum.

Owner history: Viskafors Gummifabrik AB, Trelleborg AB

Göran Spetz