InspectAPedia ^TM

Paint Sample Preparation and Analysis Pocedures
ExteriorAPedia ^©

	Enter your search terms Submit search form
	Search This Website - InspectAPedia.com

A Procedure for Preparing Paint Samples for Examination by Reflected Light Microscopy

Flat Surface View of Failing Paint Chips for Paint Failure Diagnosis

Paint chips and samples from a painted surfce can be easily mounted flat for microscopic examination, though care should be taken in selection of mounting media to be sure that the media does not react with or modify the sample. Flat mounting of paint chip samples to examine the exposed and inner surfaces is a basic step in microscopic examination and lab diagnosis of failing coatings.

Examination of the exposed paint surface in flat or planar view may disclose defects such as micro cracking, micro blistering, or contaminants. Examination of the inner, hidden, or release-surface of sample paint chips from a failing coating can provide critical information needed to state the cause of the paint failure with confidence. The inner paint surface may show wood fibers, chalked dust from the painted-on surface, or even separation of paint ingredients or surfactant bleeding which form critical diagnostic data but which cannot be seen with the naked eye. Photographs of these failures are provided in other chapters of this document.

Sectional View of Failing Paint Chips for Paint Failure Diagnosis

In addition to the examination of the flat surfaces of paint chips under the microscope, the examination of edge-view sectioned paint chips can yield important information. Yet some analysts may be unfamiliar with simple and quick procedures that permit examination of paint in this diagnostic view. It is this more unusual edge view procedure which we want to document here. We make use of a sample lamination procedure introduced by the McCrone Research Institute, Chicago, IL. McCrone offers advanced courses in forensic microscopy useful across various disciplines. (The author has no affiliation with McCrone but is a graduate of a number of McCrone's courses.)

The examination of the edge of a paint chip sample can provide critical information such as:

• The number of individual paint layers on the surface represented by the paint chip sample.
• Precise measurements of each individual paint thickness layer, and, by examining along individual samples as well as by examining multiple paint samples, the variation in paint thickness per layer can also be estimated.
• Identification of micro blisters in paint such as those caused by thermal blistering or solvent blistering in paint
• The presence of debris or mold between and in paint layers can be viewed and documented

The photographs and text here show how a paint chip can be prepared for a sectioned or edge-view by either low-power stereomicroscope, or by high power forensic microscope. Click any photo to see a larger image.

1. Photo of the basic equipment needed to prepare a sectional slice of a paint chip for edge-view microscopic examination.

2. Place the selected paint chip on top of a square of clean 6-mil polyethylene sheeting. The square can be oversized to about 1" x 1" or so as it will be trimmed later.

3. Place a second square of clean 6-mil poly atop the sample, aligning the edges to make a neat 1" x 1" sandwich of paint chip between the two layers of plastic.

4. Place the sample sandwich between two clean glass slides and atop a heating plate such as shown in the photo. You may have to experiment to find the right hot plate temperature to fuse but not over-melt or burn the poly or the paint sample so experiment with non-critical sample material first.

Simple Chemical Tests to Identify Acrylic and Alkyd Paints

The identification of a paint chip sample as acrylic or alkyd-based is important for art conservationists, but also for more prosaic paint failure investigators who examine buildings. With asstance from two experts, one an experienced paint chemist and the other, an expert art conservator, we here document the procedure.

Paint testing laboratories use either chemical methods and/or infra-red spectrometry to identify binders used in paints. Infrared spectroscopy is the most fundamental way to identify almost any organic material.

Pyrolysis GC/MSD is a useful back up method, and has been used in the art conservation field. See Analysis of Modern Paints at References below.

All organic materials have a unique infrared spectrum or 'finger print'. Some paint testing labs (Bodycote) inform us thatthe follwing combination of paint testing methods are the most precise in paint identification and can be used to reverse-engineer a paint from a paint sample.

• Fourier transform infrared spectroscopy (FTIR) to determine the type of resin in the paint
• Thermogravimetric analysis (TA) to determine the fillers present in the paint
• Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy to determine the elemental composition of the paint chip.

These tests are costly, ranging from $450. to $1000. per test per sample .

A Description of Two Simple Chemical Tests to Examine Paint Chips

Chemical tests to examine paint chips or painted surfaces, while less precise and less informative, are very quick, inexpensive, and can be used in the field as well as in the laboratory. Therefore chemicals are mainly used on site and infra-red is used in the lab.

The most common chemical methods for examining paint in the field or for a "quick lab test" are:

1. NaOH-solution will make alkyd and oil paint surfaces turn yellow, but will not affect acrylates. (4% NaOH, but KOH can also be used. KOH was used for the tests shown in photographs in this document.)
2. Ethanol will soften acrylates but will not affect alkyd and oil paints.

Mixed-base paints lead to ambiguous results: This chemical method for paint testing will not always give a definitivee answer. For example if a water-based paint is comprised of both alkyd and acrylate components the chemical test will be ambiguous.

However these tests can be unambiguous: if the surface either turns yellow with NaOH or softens with ethanol, and if the converse test of the same sample using the opposite chemical does not produce the key reaction, then the test is reliable.

We performed the tests shown in this document, followed by sending samples of the same paints to an independent paint testing laboratory for advanced testing. The results of this advanced laboratory analysis will also be reported here as a cross-check on our chemical test for acrylic and alkyd paint.

Ethanol Test on Paint Chips Separate Acrylic from Alkyd

Here are photographs showing the effectiveness of the Ethanol test on two paint chips. One paint chip remained brittle and fragile as it was at the outset, unaffected by the ethanol, indicating that the chip was not an Acrylic. We suspected it was an alkyd paint, confirmed by the KOH test. The second paint chip becomes soft after about 4 minutes in Ethanol, as we demonstrate by curling and rolling the previously fragile brittle chip using our forceps. This confirms that the ethanol-softened paint was an acrylic.

Paint chip remains flat = alkyd/oil: This paint chip remained flat and brittle, unaffected by submersion in ethanol, suggesting that it is not an acrylic paint. (We suspected that it was an alkyd or "oil" based paint).

Paint chip softens, curls = acrylic or latex: This paint chip curled when soaked in ethanol for four minutes, and was easily bent and rolled using our fine forceps as shown in the photo. This is an acrylic paint.

NaOH or KOH Test on Paint Chips to Separate Acrylic, Latex, from Alkyd

Here are photographs showing the effectiveness of the KOH test on two paint chip samples. One turned yellow (indicating Alkyd paint) and the other was unchanged (indicating not alkyd paint, in this case suspected Acrylic). [Photos coming]

Summarizing these tests: We use either chemical methods and/or infra-red spectrometry to identify binders. Chemicals are mainly used on site and infra-red is used in the lab. The most common chemical methods are:
1. NaOH-solution will make alkyd and oil paint surfaces turn yellow, but will not affect acrylates.
2. Ethanol will soften acrylates but will not affect alkyd and oil paints.
This chemical method is very crude and will not always give a definite answer (for example if a water-bsed paint comprises of both alkyd and acrylate components), but if the surface either turns yellow with NaOH or softens with ethanol, then you are in business!

Contributors & References

• Daniel Friedman American Home Service, Poughkeepsie, NY, diagnostic building investigations since 1976, forensic laboratory analysis since 1986
• Leila Kotama, Product Manager, Tikkurila Paints Oy, Finland. Dr. Kotama has more than 20 years experience as a paint chemist.
• Ulrik Runeberg, Conservador , Museo de Arte Contemporaneo de Puerto Rico, San Juan Puerto Rico
• Daniel Friedman, American Home Service, Poughkeepsie, NY, principal author, diagnostic building inspections since 1976, diagnostic lab forensics since 1986
• Bodycote Materials Testing, Ontario, Canada


• Paint and Surface Coatings, Theory and Practice, R. Lambourne & T.A. Strivens, Ed., Woodhead Publishing Ltd., William Andrew Publishing, 1999 ISBN 1-85573-348 X & 1-884207-73-1 [This is perhaps the leading reference on modern paints and coatings, but is a difficult text to obtain, and is a bit short on field investigation methods - DF]
• Analysis of Modern Paints, Thomas J.S. Learner, Research in Conservation, 2004 ISBN 0-89236-779-2 [Chemistry of modern paints, overview of analytical methods, pyrolysis-gas chromatography signatures of basic modern paints and their constituents, Fourier transform infrared spectroscopy for paint analysis, direct temperature-resolved mas spectrometry, and analysis in practice - technical reference useful for forensic paint science, focused on art works -DF]
• Seeing Through Paintings, Physical Examination in Art Historical Studies, Andrea Kirsh, Rustin S. Levenson, Materials in Fine Arts, 2000 ISBN 99-051835 [ forensic science, technical reference, focused on art works - DF]
• Paint Handbook: testing, selection, application, troubleshooting, surface preparation, etc., Guy E. Weismantel, Ed., McGraw Hill Book Company, 1981 [Excellent but a bit obsolete paint theory and practice, also a bit light on field investigation methods, out of print, available used-DF]
• Art, Biology, and Conservation: Biodeterioration in Works of Art, Robert J. Koestler et als. Eds., Metropolitan Museum of Art, 2003, ISBN 1-58839-107-8

Paint Test Laboratory Listings Welcome: independent forensic and microscopic or chemistry labs offering paint analysis or paint failure services are welcome to be listed here at no fee. See our ADVERTISING & LINK EXCHANGE POLICY and Contact Us

More Information on Building Exteriors and Other Building Diagnostic Inspections and Repairs

• Exteriors, Landscaping, & Siding - Inspection, Repairs, Product Failures

• Quotes in the opening text of this document are from the encyclopedic but not quite complete paint website: PPG Exterior Failures http://www.ppg.com/getpaint/etraining/solver/exterior.html

InspectAPedia ^TM Home & Site Map - Building Inspection, Diagnosis, & Repair, Environmental Inspection & Testing - Research Website

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Home Inspection Construction Consulting Services & advice for home buyers

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Contact Daniel Friedman for website content suggestions or for fee-paid consulting

	Enter your search termsSubmit search form
	Search This Website - InspectAPedia.com