Source: Geissinger, Karen & Krekel, Christoph. Leim aus Hecht- und Karpfenschwimmblasen – eine mögliche Alternative zu Störleim? Published in: Zeitschrift fûr Kunsttechnologie und Konservierung. 2/2007
Translation and annotations by Alexandra Neubauer and Sara Pietarinen.
Abstract
This diploma thesis examines the properties of fish glues made from swim bladders of carp and pike. A series of glues was produced by varying duration and temperature of the heating treatment. For comparison, all subsequent tests were additionally carried out with the well-known sturgeon glue. The analytical part of the thesis begins with a study of ancient sources concerning the historical use of different swim bladders for glue production. The examinations start with the determination of the glue yield rate using the different swim bladders. We will show that – compared to sturgeon glue – the yield rate of carp and pike bladders depends very much on the method of glue production. The analysis of the dispersal of the molecular weight by SDS-gelelectrophoresis shows how the denaturation of the protein chains within the glues proceeds during the heating treatment of the swim bladders. At a temperature of around 70°C the molecular weights in the carp and pike glues are clearly increasing. This means that there exists a kind of category temperature above which the protein fragments begin to rearrange into longer chains. However, the different sturgeon glues are surprisingly similar in this respect. In order to compare the tackiness of the different glues, we conducted a tensile test using glued canvas stripes. Both the sturgeon glue and the carp and pike glues show a strong dependence in tackiness of the glue producing method, although a direct correlation is not evident. Each of the fish bladder glues heated for four hours at 60°C were also examined for viscosity using a rotational rheometer. The lowest viscosity was measured with the carp glue whereas the pike glue showed the highest viscosity. Shear thinning could not be detected. A final test was carried out to examine the ageing properties of the glues by exposing both the glue films and the glued canvas stripes to elevated temperature and fluctuations of relative humidity in the hot cabinet for several weeks. In the following tackiness tests the samples did in fact show some changes compared to the « fresh » bondings. However, a subsequent SDS-gelelectrophoresis did not show any further degradation of the protein chains inside the glues.
Introduction
The sturgeon glue is celebrated as an ancient glue of the best quality since the early Middle Ages. It is preferred to use the sturgeon glue rather than other animal or fish glues in the restoring of paintings, icons and other objects.
The diploma thesis of Karin Geißinger and Christoph Krekel examines the properties of fish glues made from swim bladders of carp and pike. In this comparative research the glue yield rate, the dispersal of molecules, the tackiness and the viscosity as well as the ageing properties of the carp and pike glues were examined.
Today the sturgeon glue is mostly used for the fixing of paint layers and for the thear-to-thear gluing of canvas paintings. Even in low concentration, it has a high gluing power. However, the disadvantage of the sturgeon glue is its expensiveness, which is caused by the great demand for the product as well as by the difficult market conditions.
Sturgeon bubbles are obtained from wild sturgeons, but the sturgeon species and their provenance can’t be specified. The synonym for « Störleim » (sturgeon glue) « hausenblase » (‘Fischblase’, ’Fischleim’, eng. Isinglass) could refer to the fact that the sturgeon glue made of swim bladders is actually often made of swim bladders of different fish species. In industry, the « Isinglass » was a common term for fish glues. It was in fact the restorers who adopted the term « Störleim » (sturgeon glue). The swim bladders of carp and pike have been in use since the early Middle Ages, as it is known from the medieval literature as well as from the literature of the 18th century. Even Cenninis starting point was that the fish glue was made from various species. Besides the swim bladders, fish glue can also include skin, fish bones and other leftovers. The diploma thesis dealt with the production of fish glues made of pike and carp. The assumption that also these raw materials could be used in glue making, was based on these different sources.
The chemical differences appear through the age of the fish – depending on the time of slaughter as well as on the temperature of the environment and food. That is to say, even every species can have a different solubility of the collagens, which makes the fish breeding places very useful for this purpose. Because the fish come from the same environment, the water temperature and the feeding are the same and the fish get also slaughtered at the same age.
To sum up, the sturgeon glue is statistically spoken probably the best known and the most used glue, but it can be easily substituted with the pike or carp glues or even with the stockfish glue.
Treatment of the swim bladders of carp and pike
Getting the swim bladders of carp and pike is easy and inexpensive. Because the swim bladders would otherwise be thrown away after the gutting, the fish breeders and dealers are more than happy to give them away.
The fish used in the experiments were taken from fish breeding places. The carp is a fish that gets bred, but the pike is more difficult to breed, and if it is caught wild, it is impossible to know the age of the fish. That is why for this research, the fish was bought from the fish breeding places – they were bred in same circumstances and they were the same age. All swim bladders of the fish were well cleaned and the three different skin layers were carefully separated and dried. The carp and pike swim bladders were soaked in Hostaphan, and put in an elevated room temperature. In 24 hours the bladders were dry and ready to be used.
Making of the test glue
The first tests on the different skins of carp showed that only the white outer skin of the big bubble chamber (der grosse Blasenkammer) was usable for making of the glue. The dried bulbs were cut in little pieces and soaked in water (10%) for 24 hours. 12 different glues for each fish were prepared for the exam. They were heated from one hour to four hours at a temperature of 50°C, 60°C, 70°C and 80°C. After the heating, the insoluble parts were filtered. Finally the filtered glues were soaked in Hostaphan and dried at least for 24 hours at a temperature of 20°C and 55-60 % RF.
Material and methods: Examination of molecyle size diversion
The analysis of the molecyle size diversion shows the grade of degradation of the protein chains, which are linked with the different ways of fabrication. It seems that this is the best way to make carp and pike glue. The comparison with the sturgeon glue reveals the quality of the new products for conservation of paintings.
Gluieng power tests
For the testing of glueing power the SDS-Page-Method, the standard glueing power test, was used. The gluing power of the different glues was measured through tearing and turning test. Stripes that were glued together were prepared and the testing was made in a well preperated homogeneous climate.
Viscosity measurements
The cylinder measurement method was used in viscosity measurements Each of the fish bladder glues heated for four hours at 60°C were examined for viscosity using a rotational rheometer. The chosen temperature for the measurements was 40°C.
Ageing
Parts of the tested glue stripes were put to strong changes of temperature and humidity. The purpose was to find out the differences of the new and the artificially aged glues. The molecules were not particularly changed.
Results
Surprising was that the outer skin had the best gluing quality, because in the literature it is recommended to use the inner bladder skin. The first preparation of the sturgeon, carp and pike swim bladders showed that the glue was best received from sturgeon (95,5% - 98%) on which the temperature and the time of the fabrication did not have an effect. From carp the amount of the received glue was 62% - 81%, depending on the way of fabrication. The amount of glue made of pike, however, was only 31-60%. The difference between these glues treated in various ways was almost 50%. Die Probably this was the reason for the preference of the sturgeon glue over so many centuries. The diagrams of the molecule size and diversion show that the carp and pike glues could be brittle.
Gluing power
The sturgeon glue is the most homogeneous and powerful glue. The biggest differences were seen in glues heated only for one or two hours in lower temperatures (50-60 %°). In higher temperatures there are no remarkable differences, that is to say, the glue made from swim bladders of carp and pike approved to be just as usable as the sturgeon glue. The lowest viscosity was measured with carp glue, whereas the pike glue had the highest viscosity in thin solutions. Both the sturgeon glue and the carp and pike glues show a strong dependence in tackiness of the glue producing method
Finding an alternative to the sturgeon glue is important because of ecological reasons - the sturgeon species is in danger of extinction. This can lead to unavailability of the sturgeon glue on the market. The dried swim bladders are also expensive. Especially the carp glue could be a good substitute for the sturgeon glue. Because the preparation of the glue is easy, restorers can make glue by themselves. That way, it is not expensive and the quality of the glue can be compared to the one of sturgeon glue.