Background
The project aims to investigate the use of hydroxypropyl cellulose (HPC) combined with paper pulp as a material for filling gaps in wooden archaeological and art historical objects (non-structural).
The main brand of HPC used in conservation is Klucel. Klucel comes in different grades, which provide different viscosities. The main one used in objects conservation is Klucel G (also E). It is a white powder, dissolves in organic solvents to form a clear or hazy colourless liquid.
This project was initiated by a conservation treatment carried out on a wooden Egyptian coffin at the Ashmolean Museum in November 2011. The coffin had losses that had been filled with AJK; some AJK fills were removed, leaving large gaps in the sides. These were filled with 15% w/v Klucel G in 3:2 IMS:acetone & Arbocel BC200 (0.3mm fibre paper pulp) with pigments.
I experimented with other possible fills before deciding on this one, and I chose HPC & paper pulp because they were cellulose-based, hoping that this would be more compatible with wood than unrelated materials e.g. acrylic resin / microballoons. But it made me think – was this true? Had anyone looked at the use of these fills and their behaviour regarding fills for wood? Wood is hygroscopic and anisotropic, which can make it difficult to choose a filling material. Ideally for the coffin the fill would respond to water a bit like wood, e.g. shrinking and swelling, thereby not putting pressure on the surrounding wood (swelling) or the adhered surfaces (shrinking).
I decided to send out a survey querying what other conservators had been recently using to fill wooden objects.
The main brand of HPC used in conservation is Klucel. Klucel comes in different grades, which provide different viscosities. The main one used in objects conservation is Klucel G (also E). It is a white powder, dissolves in organic solvents to form a clear or hazy colourless liquid.
This project was initiated by a conservation treatment carried out on a wooden Egyptian coffin at the Ashmolean Museum in November 2011. The coffin had losses that had been filled with AJK; some AJK fills were removed, leaving large gaps in the sides. These were filled with 15% w/v Klucel G in 3:2 IMS:acetone & Arbocel BC200 (0.3mm fibre paper pulp) with pigments.
I experimented with other possible fills before deciding on this one, and I chose HPC & paper pulp because they were cellulose-based, hoping that this would be more compatible with wood than unrelated materials e.g. acrylic resin / microballoons. But it made me think – was this true? Had anyone looked at the use of these fills and their behaviour regarding fills for wood? Wood is hygroscopic and anisotropic, which can make it difficult to choose a filling material. Ideally for the coffin the fill would respond to water a bit like wood, e.g. shrinking and swelling, thereby not putting pressure on the surrounding wood (swelling) or the adhered surfaces (shrinking).
I decided to send out a survey querying what other conservators had been recently using to fill wooden objects.
Survey
The survey consisted of 4 main questions:
1.What have you used to fill wood in the past year?
2.What on this list (below) would you consider using to fill wood?
3.What on this list (below) would you NOT consider using to fill wood?
4.What properties do you consider to be important when deciding on materials for gap filling wooden objects?
1.What have you used to fill wood in the past year?
2.What on this list (below) would you consider using to fill wood?
3.What on this list (below) would you NOT consider using to fill wood?
4.What properties do you consider to be important when deciding on materials for gap filling wooden objects?
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List for Q 2 & 3
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List for Q 2 & 3
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List for Q 4
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Survey results
- Sent to the Conservation DistList (international), operated by the AIC, and also emails to interns and staff, and anyone I could find on the internet!
- 99 people responded
- 90% claimed to be professional conservators, and 14% conservation students (some overlap here!)
Q1. What have you used to fill wood in the past year?
- The most mentioned adhesive was B72 (41% of those who responded to the question), followed by Klucel (18%) and epoxy (15%)
- The most mentioned fillers were microballoons (51%) followed by paper pulp (22%), tissue (21%) and wood (20%)
- B72 was often teamed with microballoons, and KG with paper pulp / tissue, but also mbs with KG and B72 with cellulose-based fillers
Q2. Which of the following materials would you consider using to gap fill wooden objects?
- The most mentioned adhesive was B72 (75%), followed by HPC (42%)
- The most ticked fillers were microballoons (68%), balsa wood (59%) and paper pulp (49%)
Q3. What on this list would you NOT consider using to fill wood?
- 16% would not consider Klucel G
- 12% would not consider paper pulp, although only 5% would not use long fibre tissue
Q4. What properties do you consider to be important when deciding on materials for gap filling wooden objects?
- Most people considered retreatability to be an important factor (84%)
- Low amount of shrinkage on curing was also important (81%)
- Similar reaction to RH was thought important by 75% of respondents, and dissimilar reaction to RH by 9%.
- Respondents were split on whether the fill should have high or low adhesion to the substrate (27% vs 26%), probably because this depends on circumstance.
- Two thirds considered high flexibility to be important (then said they would use B72 and microballoons…?)
- People found this question difficult to answer because the responses are so dependant on the circumstance
Experimental
I decided to try to test some of the properties of Klucel & paper pulp (compared to B72 / microballoons). I wanted the experiments to be low tech and useful – applicable to use on practical conservation problems, and understandable to people without a PhD in physics, or access to fancy equipment.
Questions to aim to answer:
- Is a cellulose fill in a cellulose object more compatible than a synthetic fill? - Is Klucel + paper pulp an appropriate filling material for wood?
Wished to experimentally invesitgate:
Questions to aim to answer:
- Is a cellulose fill in a cellulose object more compatible than a synthetic fill? - Is Klucel + paper pulp an appropriate filling material for wood?
Wished to experimentally invesitgate:
- Shrinkage
- Drying time
- Adhesion to surface (tension)
- Compressibility/flexibility
Reaction to RH
Shrinkage
3 x concentration (3%, 7%, 12%)
3 x solvent (water, IMS, acetone)
3 x filler (0.7mm paper pulp, 0.2mm paper pulp, glass microballoons)
Silicone rubber moulds made by pouring silicone onto a perspex mould. 3mm and 6mm deep.
Leave to dry, measure shrinkage to width and depth with micrometer (3 times each)
Repeat 3 times, find averageAlso look at – adhesives with no filler; B72 in IMS, B72 in acetone with and without fillers (controls)
3 x solvent (water, IMS, acetone)
3 x filler (0.7mm paper pulp, 0.2mm paper pulp, glass microballoons)
Silicone rubber moulds made by pouring silicone onto a perspex mould. 3mm and 6mm deep.
Leave to dry, measure shrinkage to width and depth with micrometer (3 times each)
Repeat 3 times, find averageAlso look at – adhesives with no filler; B72 in IMS, B72 in acetone with and without fillers (controls)
0.7 and 0.2 refer to fibre lengths of paper pulp; mb = microballoons
Drying time
Similar layout to the shinkage test, but all the samples are cut into individual squares. For convenience, one filler was tested at one time, so 3 x concentration and 3 x solvent were the variables for each experiment. The samples were weighed to discover when they ceased to lose mass i.e. all the solvent had evaporated and they were dry.
