Sample Collection

There are two primary aspects to paint sample collection – the packaging of the samples and the collection procedure itself.

Samples are typically collected in one of two types of packages. Manila coin envelopes are highly recommended. They have large flaps which should remain unsealed. There is virtually no possibility of the sample migrating from such an envelope. The other possibility is plastic resealable (Ziploc) bags which can be opened and reclosed at will. The only drawback to this type of package is that labeling can be difficult. Under no circumstances should paper letter envelopes, sealed or unsealed, be used. If they are sent in a sealed state they have no further value once they are opened. If they are sent in an unsealed state the sample readily migrates from the envelope as the flap is inadequate to contain the contents.

The samples should be labeled during the collection process. Typical information includes the sample number, building name, building location, name of collector, date of collection, and specific data regarding the actual location of the sample. This can be written on the face of the manila envelope or, in the case of the plastic bag, can be written on it using appropriate pens or written on paper and included inside the bag.

Collection procedures vary primarily depending on the type of substrate encountered. In order of typical frequency substrates include wood, plaster materials, wall coverings, hard masonry materials, and metals. The samples are collected using a sharp metal blade such as a scalpel or XActo knife. If the latter is used, a curved blade similar to that of a scalpel works best.

Sample size is relatively insignificant compared to quality. Although actual parts of a building are submitted for analysis, the sample need not be large at all as it is viewed through a microscope. In this case, size does not matter. What is needed is a sample with all of its paint layers well adhered to each other and to their respective substrates.

There are cases in which the paint simply refuses to adhere to the substrate. Typically this happens with wood elements which were originally primed with varnish. In these cases the samples should be collected without the substrate and if varnish was used, it will appear under the microscope, confirming the original prime coat.

Most wood elements are milled trimwork. For these one should find areas with an apparent heavy paint buildup. Do not look for weathered wood, thinking that because it appears to be original, there is historic paint on it. The wood is weathered and has lost its historic finishes and, invariably, proves to be worthless. Look for areas that are relatively protected from weathering. Typically vertical surfaces are better than horizontal surfaces. Worst surfaces are areas such as window sills. In taking the sample gently cut with the grain and pry the sample loose. A broken surface to the cross section of the sample is best. If the sample is cut or sawn the paint layers become blended together. Typically, the wood splinter does not easily stop as the grain goes farther into the wood. If one finds this happening, then a countercut perpendicular to the grain can be made and the splinter snapped off at the point. For those wood surfaces without an edge sample techniques similar to those of plaster, as described below, can be used.

Except for plaster moldings, plaster surfaces tend to be flat. Samples from plaster moldings can be collected using techniques similar to those described for wood edges above. For flat areas the blade can be used to create a shallow crater, making sure that, if possible, all of the paint is well adhered to the plaster. Again, the goal is to reveal a complete set of layers with rough, broken edges. For flat wood surfaces care should be taken to work with the grain. Sometimes a thin, small, rectangular piece is cut from the wood surface.

For hard masonry surfaces such as brick, stone, and concrete the same principles apply, although execution can be extremely difficult, if not impossible. In a worst case scenario, the paint can be removed to the surface of the substrate with care being taken to take samples with complete, intact, sets of layers.

For metal surfaces there is no reasonable means of collecting the sample with its substrate. If the metal piece is small it can be removed and submitted for analysis. If not, the sample should be removed as gently as possible making every attempt to remove an intact sample. Too frequently, however, this proves to be impossible and a scraping technique must be employed. Although this results in fragments and dust, even this type of sample typically can be analyze with positive results.