To supplement stratigraphic exploration, a microscopic examination is often in order. This is the case if on-site work does not yield enough material or the stratigraphy cannot be categorized with sufficient exactitude. However, under the microscope even the smallest of phenomenon or trace evidence becomes visible.
Our microscope SMT-4 (made by Askania) delivers 17 to 67-fold magnification, meaning in our laboratory we are capable of examining coatings or materials samples down to the smallest of details.
For an examination under the microscope a sample (e.g. a coatings sample) is taken with a scalpel. This delicate process is, as a rule, undertaken by a certified conservator. Afterwards the sample is fixated in a container by means of one-component synthetic resin. Depending on the nature of the sample, two-component resin (epoxy) might also be used.
After hardening the resin under blue light (polymerization) the sample is prepared for reflected-light microscopy. For this, the block is roughened dry or whet, according to the sample’s properties. The abrasive paper used for this process features grain sizes from 40 to 12.000. After polishing, the sample is examined under the scope and then photographed or digitalized, respectively. Staining and light filters provide an even more in-depth examination.
2. Color fans
To determine historical colors on a given monument/ object, we oftentimes use color fans. Always according to the nature of the object, we use historic color fans, neutral or independent fans, or those used by manufacturers. NCS and RAL are fans in wide use independent of manufacturers, while the NCS system is the one most commonly used in restoration work. Aside from the fact that it is not tied to the range of a specific manufacturer, this system is appreciated for its systematic classification and the easy-to-handle coding. On the other hand, the RAL system delivers less variants and is, for reasons of its surface texture, seldomly used in conservation.
For color determination of mineral surfaces there are no color fans available independent of manufacturers. Color fans made by KEIM are the system of choice here.
3. Mortar analysis
By conducting a mortar analysis, historical wall and joint mortars, common and high-quality finishes/ renders, decorative finishes/ render, artificial stones as well as stucco are examined as to their composition and properties. For a sound and valid restoration or reconstruction a mortar analysis may be of the essence. As a rule, this type of analysis consists of the qualitative and quantitative determination of all materials components. It shows the ratio of bonding agents v supplements. It also determines what materials are used in the composition of bonding agents and supplements.
As a rule, we as certified conservators take samples only after we have examined and documented the materials on site. As part of this preliminary examination we asses coloring, composition, strength and texture of the mortar.
Following this, the mortar sample along with a list of questions pertaining conservation aspects is sent to a science laboratory. Standard procedure there is to solve the sample by means of HCI breakdown. Afterwards, individual materials components are determined through thermogravimetric analysis, and supplements are sifted out (determination of cut-off line).
Aside from the examinations mentioned above, other conservation-relevant examinations and explorations may be necessary as well.They are
- drill-core analysis
- assessment and monitoring of cracks, fissures and rifts
- assessment and measuring of water absorption (Karsten method)
- assessment of bond strength of coatings (according to DIN EN ISO 2409)
- further examinations on request
Some of the scientific analyses are conducted at specialized commercial laboratories. However, their processes are always closely monitored by us. This may include qualitative and quantitative analysis of salts, dendrochronological analysis, stone petrology as well as wet-chemical verifications.