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Case studies using Pemulen emulsion

Page history last edited by Nancie Ravenel 10 years, 8 months ago

At Shelburne Museum, the working method has been as follows:

  1. Emulsion is shaken in the jar prior to use and then a small amount is decanted into an open container.
  2. Using a small soft flat brush, emulsion is brushed on to the surface to be cleaned and gently agitated using the brush.
  3. Once the emulsion appears to be colored with grime, it is wiped from the surface using cotton wadding or cotton swabs.
  4. The area cleaned is then cleared with deionized water on cotton swabs.

Case study 1

Dentzel carousel panel (oil on canvas) depicting Uncle Sam and Spain

FC-7.66, Collection of Shelburne Museum

2007062423UncleSam.pdf

This was one of the first objects where we tested the use of a Pemulen/benzyl alcohol emulsion.  The painting on canvas had an uneven and very yellow varnish on the surface which was somewhat soluble in acetone.  Cleaning with acetone on cotton swabs was uneven, however.  While the Pemulen emulsion was effective in some areas, some paint colors were sensitive to water, and so other cleaning solutions were used in those areas.

 


Case study 2

Dentzel carousel panel (oil on canvas) depicting a woman walking a dog

FC-7.62, Collection of Shelburne Museum

2008062424womanwalkingdog.pdf

This was another one of the first objects where we tested the use of a Pemulen/benzyl alcohol emulsion. Like the Uncle Sam carousel panel, this painting also had a very uneven and yellowed surface coating.  Additionally, the front and back of the canvas had been splattered with black machine oil. The oil on the back of the canvas had migrated through the paint and varnish to the surface of the painting, appearing as solid black dots.The thick black oil was thinned from the back to the canvas before working from the front to remove the oil that had penetrated through.  Examination of the paint showed that the oil had migrated through fissures in the oil paint, much in the way filliform corrosion grows through micropores in coatings on metal. Both Carbopol gels and Pemulen emulsions were tested for cleaning the front of the painting.  Bulking Carbopol gels with inert absorbtion materials (cellulose powder, Attapulus clay) were also tested as a possible poultice material for removing machine oil from the canvas back.

 


Case study 3

Wood train (oil paint on wood)

1977-45, Collection of Shelburne Museum

2008052513modeltrain.pdf

The painted wood train had a grimy layer of wax on top of the glossy black paint.  While an application of petroleum distallates on cotton swabs followed by 2 % ammonium citrate in deionized water was slowly effective at removing the grimy wax, petroleum distallates emulsified into a Pemulen gel made with TEA and 2% TRIS was more effective, working more quickly and evenly than the two step system of using petroleum distallates followed by ammonium citrate.

Comments (2)

Dale Kronkright said

at 12:03 pm on Jun 30, 2009

In the GCI Solvent Gels book, as well as in Wolbers’ Aqueous Methods and many of the serial research published on polyacrylic acid, there is evidence that clearance of gel residues ideally involves a pass using a solvent related to the gel solvent. It may be wise to clear with benzyl/isopropyl mixture, since water will only clear ionic and polar residues, rather than residues having an affinity to non-polar paint substrates. Thoughts from you and your workers?

Nancie Ravenel said

at 10:47 am on Jul 10, 2009

Interesting thought, Dale.

Apart from the painted surface of the train, most of the objects that we've cleaned - elements from the Dentzel carousel - have had a discolored varnish under the linseed oil. We've noted that the Pemulen gels and emulsions are only partially effective in removing these discolored varnishes. As a result, when working with the objects from the Dentzel carousel, its not atypical to reduce the layer of linseed oil as a first step using a Pemulen gel or emulsion and then we may use something else, acetone, ethanol or a benzyl alcohol Carbopol gel rinsed with isopropanol/petroleum distillates to reduce the thickness of that varnish. So at least with the Dentzel carousel, that solvent pass happens in order to reduce that lower layer. But obviously that's not the case for everything.

One thing I am very interested in is reformulating these gels and emulsions using ammonium hydroxide rather than TEA to see if they could be as effective with the thought that there would be less potential of ammonium hydroxide being left as a residue than TEA.

I wonder if there's less potential for leaving a non-polar residue behind when using Pemulen since the polar elements of the microgel have been determined to surround the non-polar elements. (see for instance Maria Scucs et al., “Thermoanalytical and microscopal investigation of the microstructure of emulsions containing a polymeric emulsifier,” Journal of Thermal Analysis and Calorimetry 94, no. 1 (October 2008): 271-274.) A logical question is whether the combination of steric and hydrogen bonding forces in the mocrogel would be enough to minimize the chance of leaving non-polar residues on the surface.


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