Characterization & Analysis of Surface Finishes

Material characterization and analysis in the context of the Cliff Palace conservation program were undertaken to describe the microstructure and chemical composition of the earthen finishes in order to better understand their original appearance and basic properties, especially as the latter relates to decay processes and remedial and preventive treatments. Not addressed during this study were archaeometric issues of raw material sourcing (provenience) or age.

Treatment supervisor collecting samples for analysis, 2001.

The eighteen priority spaces at Cliff Palace were studied and analyzed with the main focus of the analyses on Kiva Q, Kiva K, Room 121 and Room 64. These were chosen as representative spaces to further explore the relationship between space type and surface finishes. Microstructure and chemical composition were studied through a comparison of successive layer sequencing (i.e., stratigraphic analysis). Polarized light microscopy, reflected light microscopy, quantitative image analysis, and x-ray diffraction were also performed to analyze selected samples from the above spaces in advance of treatment.

According to the Architectural Finishes Treatment Priority Assessment, Mesa Verde National Park, 1998-1999, the following high priority areas in Cliff Palace (5MVO625) were selected for treatment. Mortar and surface finishes samples were taken from the 18 selected spaces:

• Kiva H
• Kiva J
  
• Kiva K
  
• Kiva N
  
• Kiva Q
  
• Open Area J: Exterior facades rooms 25, 26, 27
  
• Open Area M and Open Area 6: Exterior facades rooms, 40, 41, and 42
  
• Open Area R: Exterior façade room 64
  
• Open Area 42: Room 58
  
• Open Area 25 and Open Area 26: Speaker Chief House:
  
• Exterior facades of rooms, 70, 71, 72
• Room 121: Square Tower
  

Graduate student prepares samples in field for laboratory testing, 2001.

Sample locations were selected according to representative architectural elements, visible schemes, and condition (i.e., protected areas displaying existing damage were preferred sample locations in order to reduce damage). Samples were extracted with a scalpel and varied in size from 0.2g to 100g depending on the situation. The sample location and number were recorded on field photographs and in schedule form. Given the fragile nature of many of the multi-layer samples, specimens were carefully packed in individual glass and plastic sample vials in cotton and clean sand and labeled. Samples taken in previous years were merged and renumbered according to the final sample list. Sample locations were then indicated on the treatment photomontage elevations for each space.

All bulk samples from the 18-priority spaces were examined under a Nikon SMZ stereomicroscope in normal reflected light. Physical properties such as texture, hardness, color, size, shape and weight were noted. The samples were then compared and grouped per space by location, and sample type (e.g., modern repairs versus historical repairs). Selected representative samples for each space were embedded in a polyester-acrylic mounting medium (Bioplast®) and cross-sectioned with an Isomet® micro saw. Samples from Kiva Q, Kiva K, Room 121, and Room 64 were further analyzed in greater detail through thin section analysis. The thin-sections were vacuum imbedded with blue dye and stained with alizarin crimson to indicate pore space distribution (blue) and the presence of calcite (red).

Microscopical Analysis
All analytical techniques have limitations and hence several methods are needed to complement and confirm results. Through gross visual examination and low magnification reflected light microscopy, the color, texture and initial description of the finishes were recorded. Further examination of whole sample thin sections with polarized light microscopy (PLM) revealed both the microstructure and fabric of the mortars including stratigraphy, determined the relative ratio of matrix and aggregates, and identified the morphology and mineralogy of the aggregates. X-ray diffraction was utilized to identify the mineralogy of the fine clay and silt fractions comprising the paste.

Treatment supervisor working on sample analysis using Bio-Quant software at the Architectural Conservation Laboratory, University of Pennsylvania, 2001.

Image Analysis and Micromorphology
Image analysis [Bioquant Nova® for Windows, 98 BQ Nova Version 5.00.8 MR (R&M Biometrics, Inc.)] was used to better characterize the geo-physical properties of the samples. Since gravimetric analysis is not possible on these small-layered samples, image analysis provides a non-destructive method to study and describe the various components such as the ratio of matrix (paste) to aggregate. A micro-morphological description of each layer per sample was prepared to support numerical and visual results from the image analysis software and allow quantitative comparison of layers within a sample, samples within a space, and samples across spaces and sites.

Micro-morphology is a unique technique for the study of multi-phase composite materials: soils, mineral formations and transformations, and man-made composites such as mortars and plasters. The microstructure of a plaster or wash is the spatial distribution and total organization of the plaster/wash system as expressed by the degree and type of aggregation and the nature and distribution of the pores and pore space. The matrix or paste of the plaster and washes forms a more or less continuous phase, which encloses coarse material concretions, etc., and has been quantified for every plaster finish layer. Basic micro-morphological concepts recorded included fabric, matrix and structures.

The Bioquant ® Basic toolkit provides morphometric measurements and topographic maps of hand traced areas, distances and object counts. It can be used with or without a video camera. Customizable data structure allows the addition of an unlimited number of user-defined calculation arrays, as well as multiple measurement arrays of the same type. Array names are customized to reflect the features measured.

Instrumental Analysis
X-Ray diffraction analysis (XRD) was performed as the method of choice for identification of the mineralogical species of the clay/silt fraction. Previously, representative finish samples from Kiva Q and Kiva K, Cliff Palace were analyzed by George Austin of the New Mexico Bureau of Mines and Mineral Resources in April 1999. The current analysis was performed with a Rigaku D-MAX diffractometer at the Laboratory for Research on the Structure of Matter at the University of Pennsylvania. The divergent slit and the scatter slit was 0.3mm, the receiving slit and the detector was 1 degree. A copper tube mono-chronometer was used. Bulk samples were crushed in an agate mortar and pestle and dry sieved. For matrix analysis, particles less than 2mm were sedimented on glass slides. For aggregate analysis, unoriented grains were mounted on an adhesive taped "sticky" glass slide.