Volatile Binding Media
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Contributors: Amy Davidson, Rachael Perkins Arenstein
Copyright: 2016. The Objects Group Wiki pages are a publication of the Objects Specialty Group of the American Institute for Conservation of Historic and Artistic Works. The Objects Group Wiki pages are published for the members of the Objects Specialty Group. Publication does not endorse or recommend any treatments, methods, or techniques described herein.
The information on this page was primarily gleaned from the Subliming Surfaces: Volatile Binding Media in Conservation Conference and Workshop, Cambridge, UK 15-17 April 2015 Conference Program Poster Presentations. The conference was also reviewed by Tony Sigel, Conservator of Objects and Sculpture, Harvard Art Museums and published in ICOM-CC Scientific Research Working Group Newsletter, Vol. 1, No.1, 2015. It is posted on the AIC Blog with permission of the author .
This conference marks twenty four years of CDD in conservation. It was organized by Christina Rozeik and Sophie Rowe, two objects conservators associated with the Fitzwilliam museum in Cambridge as a follow-up from an important paper they coauthored in 2008, which reviewed the first 12 years of CDD in conservation.
Rowe, S., and Rozeik, C., The uses of cyclododecane in conservation. Reviews in Conservation 9 (2008), 17-31.
The conference was attended by 72 conservator delegates, mostly from UK and Europe, with quite a few from Lithuania and several from the United States. Areas of conservation included wall paintings, architecture, stone, archaeology, ceramics, paper and textile conservators. Additional poster and oral presentations were given by fossil preparators.
- 1 What are VBMs?
- 2 Cyclododecane (CDD)
- 2.1 CDD Uses
- 2.2 CDD Application
- 2.3 Techniques for Speeding or Slowing CDD Sublimation Time
- 2.4 VBM Use in Fossil Preparation
- 2.5 Interactions
- 3 Menthol
- 4 Health & Safety
- 5 References
What are VBMs?Volatile Binding Media (VBM) are waxy solids that sublime (pass directly from a solid to a vapor phase) at room temperature. VBM can refer to a variety of subliming materials including menthol and, in conservation most commonly, cyclododecane (CDD or also sometimes abbreviated in German as "Cyclo"). VBMs were introduced to conservation in 1995 and have proved to be very versatile. Since then, the use of CDD has spread through many fields of conservation, archaeology, and since 2004, in vertebrate fossil preparation.
The conference keynote speakers, Hans Hangleiter and Leonie Salzmann, presented a talk entitled Twenty Years of Volatile Binding Media. Hangleiter reported creating his own VBM in 1985 “using liquid nitrogen to transform liquid xylene into a solid waxy material” in order to consolidate fragile mortar.
N.B. The terms sublimes and sublimates are both used to refer to VBMs property of passing directly from a solid to a vapor. Following the usage in Rowe and Roseik (2008) the proper term is sublimes.
Cyclododecane (a cyclic alkane hydrocarbon C12H24) is a wax-like substance that passes from a solid state directly to a vapor at room temperature, disappearing and leaving virtually no trace. The ability of this material to sublime has led to its increasing use in the field of art and artifact conservation as well as fossil preparation.
CDD is now considered a standard method of consolidating archaeological artifacts and skeletal remains before “block lifting”. It is less commonly used for “field jacketing” in paleontology although it has been experimented with and its use should be further investigated. The following conference talks referenced field consolidation uses for CDD:
- Use of cyclododecane in a Swiss archaeological context: questions, evaluations and more questions talk presented by Frederique-Sophie Tissier.
- Review of the long-term use of cyclododecane in archaeological field conservation at Abydos, Egypt talk presented by Lucy-Ann Skinner and Hiroko Kariye.
- Volatile binding media: exploring alternatives to cyclododecane for archaeological block lifting poster presented by Katherine Langdon, Aaron Shugar and Lucy-Anne Skinner
- Juggling fire without getting burned: working with CDD in Olduvai Gorge poster presented by Renata Peters and Eri Ohara Anderson
Counteract Out-Migration of Consolidants in Solution
This was not mentioned at the conference but the use of CDD as a hydrophobic (non-polar) sealant raises the possibility that it could be applied (molten) immediately after consolidation of a porous specimen with a resin consolidant (eg. Butvar B-98 in ethanol). This could act to prevent the solvent from pulling the resin back out by preventing evaporation at the surface. Experiments by fossil preparator A. Davidson using mock-ups with cups of loose sand appear to show some promise (personal communication, 2015).
Possible digital image enhancement
This was reported by Jackson et al in their talk entitled “Cyclododecane as a reversible contrast enhancer for the terahertz imaging of frescoes”. Terahertz imaging is the technology used in airport security body scanners.
The use of double boilers to melt CDD is standard recommended practice as a safety precaution due to the low flash-point of CDD. This can be easily done on a hot plate with CDD in a glass beaker within a larger glass beaker filled with water. Temperature can be monitored with a thermometer in the CDD and should be kept below 176 degrees F.
Two conference presentations mentioned adaptations for using CDD in field conditions. Skinner and Kariye use a portable gas burner with a double boiler for hot, dusty environments in Abydos, Egypt. In very windy and primitive field conditions in Oldovai Gorge, Peters and Anderson melt CDD in a glass beaker in a pan of water over an open fire contained within a rock fire ring. For safety the fire must be a distance from the block. To keep the CDD molten as it brought to the block, the glass beaker is placed in a container of hot water within a small makeshift insulated cradle box (of cardboard, cotton wadding and aluminum foil). The box may be held in one hand while brushing with the other hand. Use of the insulated box and also preheated water in a thermos assist in keeping a steady supply of molten CDD as work proceeds.
Addition of white spirit to molten CDD enhances the working properties during brush application perhaps by slowing set time. White spirit is less toxic than naphtha as a solvent for CDD (S. Rowe personal communication, 2015) Conference workshop participants had the opportunity to compare brush application of molten CDD with 10% added white spirits with pure molten CDD, and found the CDD-solvent mixture easier to manipulate (A. Davidson, personal communication, 2015) it was much easier to apply. Participants also found that the molten menthol was had easier application working properties than pure molten CDD. PHOTO
Molten Application Application/Manipulation Techniques
Pipetes can be used to transfer molten CDD. Glass pipettes are preferable to polyethylene (PE) due to possible reaction of CDD with PE (see below). However, the rapid cooling time of pure molten CDD makes application by pipette challenging and heating applicator tools may be preferable.
Several electric heated applicators were highlighted in conference presentations:
- The MaxWax and Speedy Wax brands of lightweight battery operated wax pen can be purchased through jeweler’s supply stores (PHOTO).
- The ECG brand 45 watt desoldering iron has been used in fossil preparation (G. Brown). It comes with a rubber bulb to suck up molten solder and the rubber bulb may be removed or pierced and a tube for compressed air installed. The flow of air may be regulated with a dental foot pedal. The air passes through a heated nozzle to provide a very localized and controllable stream of warm air. (PHOTO)
- Electric kistkas (Ukrainian Easter egg decorators) are useful for micro-applications and come with various size tips. They are available from Ukrainian specialty stores (Surma) or online retailers such as Amazon (although they seem not to be available in the UK). (photo)
- The Willard controller type E heated spatula with temperature control is available with a kitska-like tip as well as larger reservoirs for this tip (S. Rowe personal communication). This tool, while expensive, has wide application in conservation. (PHOTO)
CDD is also available as a canned spray supplied by Kremer pigment. The force of the spray may be too strong for some delicate or friable surfaces. Holding the can further away from the substrate, results in a fluffy, snow-like deposit. It is possible that this “snow” had possibilities for re-working by compressing or melting in place. The spray is more expensive than molten CDD and is purported to not contain any solvent.
Techniques for minimizing crystalline structure and maximizing density
Minimizing crystalline structure in application of CDD is important for situations where a dense application is necessary (e.g. in fossil preparation where CDD may be used as a dense filler and sealant to prepare porous specimens for molding in silicone rubber). Rapid solidification of molten CDD appears to be the most effect way to minimize the growth of crystals. Menthol was proposed as a denser, more workable fill material for molding (S. Rowe personal communication). The poster presented by VonsStein Murray et. al. entitled “Visualizing Cyclododecane on Porous Materials Using Cryogenic Scanning Electron Microscopy” exhibited SEM images of porous samples treated with a solution of CDD (in Shellsol OMS) showing no crystal formation at all, but rather a “fairly uniform coating that closely mimics the topography of the substrate”. As CDD in solution is commonly observed to grow crystals as the solvent evaporates these results were intriguing and worthy of further investigation.
Techniques for Speeding or Slowing CDD Sublimation Time
It was noted frequently during the conference that sublimation is sped with increased temperature and airflow. Suggestions included:
- Use of infrared heat lamps and fans.
- For more localized warm air flow, my coauthor Greg Brown uses a modified desoldering iron to pass a stream of compressed air through a heated nozzle to help speed sublimation of CDD trapped in deep pockets (this tool was described in our talk).
- Our talk also covered the use of a battery operated wax pen for microscopic warming and sublimation- this acts almost like a CDD eraser on a micro scale.
- I was intrigued by a mention of CDD sublimating very quickly in a vacuum. This was in a poster entitled Most fossil preparation labs have vacuum chambers for de-airing silicone rubber for molding, so this might be something to experiment with, if the specimen can withstand the vacuum.
- Sometimes mechanical removal, melting and soaking into tissue or even dissolving with white spirit can be a faster way to reduce the bulk of the CDD, leaving the remainder to sublimate.
Techniques for slowing sublimation for longer storage of stabilized objects included:
- It was noted frequently during the conference that sublimation is sped with increased temperature and airflow, implying that storage wrapped and in cooler temperature may be effective.
- wrapping with aluminum foil, bagging in polyethylene and then boxing (Skinner and Kariye talk on Abydos archaeology)
- barrier layer of aluminum tape purchased from a hardware store ( Raffler et. al. talk on mounting surface sensors on historic buildings)
- Marvelseal 360 oxygen barrier film attached with aluminum tape (Hensick et. al. talk on fresco protection at Harvard) This is food industry product used in paleontology for creating anoxic storage environments for pyrite-diseased specimens (Link) N.B. Marvelseal has a polyethylene surface that may react with CDD (see interactions below)
How do you know the CDD is gone?
The simplest way to know when all the CDD that you have applied to an object has sublimed is to weigh the object before treatment and then monitor the weight during sublimation (S. Rowe response to discussion question).
VBM Use in Fossil Preparation
The talk “Cyclododecane and Fossil Vertebrates: Some Applications for Matrix Removal, Moulding and Shipping”, coauthored by A. Davidson, R. Arenstein, G. Brown, J. Groenke and M. Brown gave an overview of the use of CDD in fossil preparation since its introduction in 2004. Included were projects covering:
1) temporary embedding of small specimens onto a working mount, as a substitute for Carbowax (G. Brown and Davidson) 2) filling deep cracks after consolidation, aided by localized warming with a modified de-soldering gun (G. Brown) 3) thorough impregnation of very porous matrix, aided by heating with a lamp (G. Brown) 4) “hot prep” of impregnated matrix using a sharpened electric wax pen (G. Brown) 5) temporary transfer by embedding a half-prepared specimen in a plastic container of molten CDD (G. Brown) 6) as a heavy coating layer in combination with plaster bandage, for support (G. Brown) 7) combined with Tietex polyester fabric as a support resistant to preparation and consolidation (G. Brown) 8) as an acid resistant filler, sealant and mask for formic acid preparation of calcareous matrix (Groenke)
9) testing of CDD as a micro-void filler for molding small specimens (Arenstein and Davidson) 10) applied in Naptha solution to seal very porous matrix for large-scale molding with silicone rubber (G. Brown) 11) as a stabilizing, protective coating for shipping delicate specimens, applied crystal by crystal and melted in place with a battery-operated wax pen- could be capped with Carbowax to delay sublimation (M. Brown and Davidson) 12) safety concerns specific to how fossil preparators use CDD
How is CDD use in fossil preparation different than other fields?
My impression was that fossil preparators are doing more work with CDD under the microscope than in other fields. CDD seems also to have more various applications in fossil preparation than in other fields, which may be a reflection of the variety of problems that fossil preparators encounter.
Rowe and Rozeik reported in their talk that, after an initial flurry of experimentation with CDD in many fields of conservation, it is now most commonly used in conservation of paper, stone and wall paintings. This conference was intended to promote information sharing as some treatment uses may be underrepresented in the published literature and, as Rowe and Rozeik pointed out, informal on-line publications often eventually become unavailable and may not be the most effective long-term methods to share knowledge.
Reactions with Polyethylene (PE)
A number of conference participants reported problems with CDD reacting with PE. These included reports of residues after applying molten CDD with PE pipettes (Tissier talk). This was said to be reported in a paper by Jaegers in the journal Restauro. Skinner and Kariye reported a Correx (polypropylene?) box containing an object treated with CDD that bowed over time, and also Tupperware (PE?) containers warping so that lids no longer fit. It was noted that Kremer Pigment, a major supplier of CDD, sells it in PE bags.
Reactions with Resin Coatings
CDD MAY DISSOLVE SOME RESIN COATINGS – One participant reported an interaction between CDD and the surface of an oil painting. It was noted that CDD can act as a non-polar solvent on oil binding media and other resins.
Sophie Rowe provided information about menthol during her talk entitled Subliming surfaces: the first 20 years on Menthol as an interesting alternative VBM. Some interesting properties include:
- Menthol has faster sublimation rate than CDD
- Menthol has a lower melting point than CDD. Menthol used as a field consolidant in Abydos did not solidify in the hot conditions (Skinner and Kariye talk)
- Molten menthol does not solidify as quickly as CDD and thus is easier to apply by brush.
- Unlike CDD, which tends to solidify as an open structure of needle-like crystals, menthol forms a dense, even film that would probably be better than CDD as a mold release or filler for molding with silicone rubber.
- Unlike CDD, menthol is soluble in polar solvents, so it would not be good for applications requiring water-resistance (such as acid preparation of calcareous matrices). Compatibility with water may allow menthol to be used as a field consolidant for wet conditions.
- Menthol is more of skin/eye irritant than CDD (Adlem) and it is smelly.
Health & Safety
While this has been a creative explosion of uses since the introduction of CDD, there have been ongoing concerns about lack of safety information and careless handling of this material, particularly regarding respiratory safety precautions. CDD is non-poisonous, lipophilic and accumulates in fat cells and the liver (Adlem talk). CDD is considered safe providing common sense measures to minimize the dose by means of respiratory protection are followed.
Respiratory protection was discussed by Frederique-Sophie Tissier in her talk entitled The use of cyclododecane in a Swiss archaeological context: questions, evaluations and more questions. She presented results of studies of exposure levels for three indoor and four outdoor scenarios for Swiss archaeologists working with CDD. The same results were published by Vernez et al., 2010. Cyclododecane exposure in the field of conservation and restoration of art objects.
- Fume hoods are an effective means of reducing exposure to CDD vapors. Respirators with organic vapor cartridges are also effective.
- Working outdoors without a respirator does not reduce exposure.
- CDD vapors are heavier than air, as are most solvents (Adlem response to discussion question.).
- Elephant trunks need to be positioned very close to the vapor source (around 10 cm to be very effective. Effectiveness drops rapidly beyond that (S. Rowe pers. comm).
- For bench work outside the fume hood, the best extraction is a downdraft system for fumes (not particles) (Adlem pers. comm.). This creates a laminar flow of fumes along the bench surface away from the worker.
- It makes sense to be mindful of high dose occupational scenarios such as opening a cabinet or drawer which has trapped a concentration of CDD vapors subliming from treated objects (N. Odegaard, pers. comm.) Odegaard is an expert on poisons in museum environments (see Odegaard et al., 2005. Old Poisons, New Problems: A Museum Resource for Managing Contaminated Cultural Materials)
- CDD has not been tested occupationally and is unlikely ever to be tested for such use specifically by conservators and fossil preparators. (Nancy Odegaard pers. comm.)
Rowe and Rozeik, 2008 anticipated accelerated investigation of the hazards associated with CDD, with the introduction of REACH (Registration, Evaluation, Authorization and restriction of Chemicals) to the European Union in 2007. As of 2015 this has not been the case (Rowe and Rozeik pers. comm.)
- A talk entitled How VBMs behave in the environment was presented by Markus Kalberer (University of Cambridge). In summary, the conclusions of this talk were that CDD, being volatile and insoluble in water, ends up mostly as an aerosol in the atmosphere, where, like most organic compounds, it is broken down by UV light and attack by reactive radicals into reaction products with much lower volatility and higher water solubility. This decay happens quickly (one day or less). “Aerosol formation from CDD is negligible (around 107 times smaller than from other sources).” Kalberer concluded that “Overall CDD is a very minor component in the atmosphere compared to the large number (and amounts) of other organics”.
What makes a chemical dangerous?
The talk entitled Cyclododecane: How Dangerous is it?' was presented by Martin Adlem, a health and safety consultant. The following is a rough outline of the talk:
1. The effect on the body
- burns or physical damage
- interference with body processes (eg. carbon monoxide)
- building up in specific organs (eg. lead)
- damage to specific organs (the liver is a common target)
- genetic damage (enters DNA)
2. The route of entry
- Skin and eye contact
3. The dose
- All substances can cause harm if enough gets into the body. The smaller the amount required to cause harm, the greater the risk. The goal is to make the risk acceptable.
How dangerous is CDD? (according to the industrial literature)
CDD is not poisonous - CDD has been tested by subcutaneous injection into populations of mice and by feeding it to populations of rats, to determine the lethal dose (LD) required to kill half the population. These are the results:
- LD 50, subcutaneous mouse > 10,000 mg/Kg
- LD 50, oral rat >10,000 mg/Kg
Scaled up to the weight of a human being, this is the equivalent of around 700 grams.
CDD is not corrosive - Testing using artificial skin has shown no evidence of corrosive or irritant properties
CDD is not mutagenic - CDD had a negative Ames test. Testing for mutagens are done on insects
CDD has a high likelihood of bioaccumulation - CDD is hydrophobic (one of its many useful properties) and conversely, lipophilic (fat-loving). It will absorb through the skin and through the lungs. Once CDD has entered the body it is not eliminated but is absorbed into the fat cells. Testing has indicated that there is a high likelihood of bioaccumulation in fish.
Other Health & Safety Tips
- Double boilers are recommended for melting due to low flash-point.
- Nitrile gloves are recommended for working with CDD.
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- Rowe, S., and Rozeik, C., The uses of cyclododecane in conservation. Reviews in Conservation 9 (2008), 17-31.