Mason Monterey Horseshoe-back Chairs at the Oregon Caves NM, 1

MPF Conservation conserved and/or restored two dozen pieces of Mason Monterey furniture from the Chateau at the Oregon Caves National Monument (NPS); this page features the Mason Monterey Horseshoe-backs or Barrel-backs.

There are several Horseshoe-backs at the Oregon Caves NM, each in a state of disrepair exhibiting condition issues which threaten the efficacy of the historic paint, leather upholstery, and wood structure, shown left in the Chateau Lobby.

MPF Conservation was tasked with conserving two, shown below after treatment: the Blue Geometric Horseshoe-back (far left) and the Floral Horseshoe-back (far right) for the Museum Collection. Rather than choosing one to feature, because they had different issues, we are combining the post into this one on both, and will indicate which we are working on throughout.

Mason Monterey geometric and Floral Horseshoe-backs after treatment in our studio, above.

The biggest issues on these beautiful chairs was:

  1. greasy dirt buildup on the finish;
  2. losses on the finish, or potential losses;
  3. original leather seats had red rot;
  4. the lacings were degraded (and even missing in the Floral chair).

We encountered only one structural issue, which was a crack on the underside of the right-facing arm on the Floral Chair, above left. This was repaired before we began the finish infill by introducing gap-filling consolidates into the splitting wood substrate using warm hide glue.

Finish: Cleaning

Greasy dirt and finish losses went hand in hand in many cases, though they are separated out because they are a two step process. The first step is to remove the dirt, fats, and grime, because this exacerbated finish degradation, threatening complete loss of the historic paint.

Above, testing cleaning solutions on the Floral chair, left, and right,
three sample swabs in order: Triton X, Stoddard Solvent, and distilled water.

Because of the severe degradation of the finishes we tested three cleaning solutions to see which cleaned the best with the least amount of loss. Some paint loss was expected during the process, because grime had worked its way underneath the finish in some areas. In these areas the lifted painted finish literally slid off the smooth wood of the chair. We tested Triton X, Stoddard Solvent, and distilled water. (See notes at bottom for solvent info.)

We chose to clean with distilled water for three reasons:

  1. It cleaned as well or better than the chemical agents and left no residue;
  2. We did not have to wear a mask during the extensive cleaning process (on these and other Mason Monterey items);
  3. No toxic chemicals to dispose and no safety issues.

MPFC used boxes of cotton swabs in the cleaning of these two chairs. The reason swabs were used is they pinpoint a small area to clean rather than rubbing with a larger cloth, so less damage is done overall, much in the way fine art is cleaned, one swab at a time.

We began cleaning the Floral Chair. In the rows above, a straightforward cleaning was performed on an arm stile and on the horseshoe top with minimal losses.

On the legs, however, there was more than simple grime. Without testing (a costly endeavor when not necessary) the grey accretions seen left, above, appeared to be an old mold infestation. The removal of this “mold” happened easily, but because it wicked under the finish, paint loss also occurred.

One thing we could not determine after cleaning was the design that was on the top of the Floral arm-tops. Dark blue, which is present on other designs on this chair, is clearly shown, right, however, the design is not discernible. It does not appear to be a ring as shown in the Geometric images below, but something larger. If we had a better indication we might have attempted an infill on the arm-tops in this area.

Cleaning the Geometric chair was much more straightforward. The only areas where we experienced more losses due to cleaning were on the arms, shown above. The grease from hundreds of hands, many of whom had lunched at the Chateau and did not wash after, embedded that grease into the paint; loss was inevitable. On the back (and other similar areas) little loss occurred with cleaning, shown right.

Finish: Adhesion

Areas of painted finish were flaking; MPFC wanted to adhere as many pieces as possible. Because these chairs were going into the Museum Collection, we felt this was a viable option; no one would be sitting in them again.

Golden’s Hard MSA Varnish was chosen after discussion with the conservation team at Golden Artist Colors.

Right, a large chunk of paint was lifting. Kate gently lifted the paint and used a thick application of MSA under it, then pressed it into place. This treatment was performed on all flaking fragments over 1/8-inch, of which there were many on both chairs.

Secondly, MSA was brushed onto the surface of the flaking paint in an effort to consolidate the finish. So much of the Floral chair was either losing finish or flaking that it was necessary to apply consolident to most of the surfaces in order to sae the historic painted finish.

The Geometric chair finish was in better condition. The area where consolidation was essential was on the large front stretcher, shown above left, where many layers of paint created the motif. It was likely the many layers of historic paint, coupled with the porous nature of the alder wood, that made it susceptible to cracking and lifting.

However, there were anomalies on the geometric chair, such as large drips of what appeared to be wax, which we gentle scraped off the legs. How wax got deposited on the legs is unknown.

Finish: Infill

Once the finish was cleaned, decisions about infill were made. The primary factors in our decision were:

  • How did infill help or hinder preservation;
  • How did infill contribute to the story of the design intent

After that, how much infill on which chair was necessary to achieve our goals?

In consultation with the curator, Mary Merryman, we decided to infill only the Floral chair, and only when it helped visitors to see the designs intact.

Right-facing leg after infill, shown right.

Also, while normally it is not advised to paint over MSA, after discussion with the Golden Conservation staff we decided to infill with Golden Acrylic paints, not historically accurate oil paint. Golden’s consultants felt for the small amount of acrylic paint infill that would be going over MSA in this scenario, it would be fine. Note: All this was discussed prior to the application of MSA.

Oil paint does not bind well with MSA varnish, which is often used over oil paint as a final coat. Also, it was decided to not quite match the oil paint color. The change would be discernible to the curatorial staff but not to a visitor (see color board below). We documented areas of infill in our treatment reports, but the ever so slight shift in color allowed staff to easily “see” the areas of infill if they looked closely. As a museum piece the requirements for conservation treatment are different than for a piece that is to be used daily.

Two colors of Straw Ivory undercoating were used before a glazed topcoat was applied to give the infill on this leg a more authentic appearance from afar.

Blue and a celery color were infilled, shown above and below, and topped with a glaze. The floral design was completed, as well as the leaves, on both the feet.

When the red and blue were initially applied at the Mason factory it was a lively free-form swirl that mixed the paints as they combined in the swirl. For Kate to perform infill the paint colors had to be continually mixed and dabbed into losses, taking into account the final topping with a Smokey Maple glaze.

Notice we did not apply infill up onto the entire front stretcher, but just to the edge of the wear pattern across the top and along the bottom. We wanted the stretcher to appear as if it was well-appointed, historically accurate and preserved.


  • Triton X-100 is a nonionic surfactant, it can also be used as a detergent and it is considered 100% “active” and biodegradable in liquid form. It has numerous general uses as a wetting agent, emulsifier or even as a mild detergent.
  • Stoddard solvent is a form of mineral spirits; however, not all forms of mineral spirits are considered to be Stoddard solvent.
  • Golden’s Hard MSA Varnish (MSA) Is considered toxic in several ways and so, while a mask is not required in al situations, due to the prolonged use and close working proximity, Kate wore a full mask when using.

Next posting deals with the leather issues, and a final round of before and after treatment.