"Yukon Seasons" Restoration - Phase 6 - by Valery Monahan, Conservator
October 31, 2008 Filed in: Yukon Seasons Heist
I have two subjects in this update: snot tape and a lock-out. Things have been running so smoothly with this treatment! It seems only fair that there be a few challenges before the finish. And here they are ... first:
The Snot Tape
I asked the folks at the Canadian Conservation Institute in Ottawa about snot tape. I wanted them to comment on its suitability for securing heavy sculptures over the long term. No one has ever asked CCI about snot tape before, but conservators ask them things about art/artifact related materials all the time and they were happy to help. They requested a sample to analyze. Commercial products like snot tape rarely come with a full ingredient list. Analysis helps provide a complete picture of the product, necessary for understanding/predicting its behaviour. I cut a small bit of old snot tape from the Yukon Seasons' mount and sent it to them.
The analysis is done and CCI has sent a report back to me. The results are as follows: the adhesive used to secure Yukon Seasons is a styrene-butadiene rubber with pentaerythritol ester of rosin as a tackifier. There was no evidence of acrylic or fibreglass in the sample. This means that while you may be using Scapa 4450 snot tape now, the stuff you got from the film crew for Yukon Seasons must have been a different brand. Scapa 4450 manufacturing information specifically states that it is acrylic and that it contains fibreglass as a strengthening agent.
According to the CCI report, the ingredients in the Yukon Seasons snot tape are consistent with many commercial pressure-sensitive adhesives. Pressure-sensitive adhesives are designed for temporary use. In this formulation, the tackifier will oxidize readily, losing tack and becoming yellow and brittle over time. It is hard to predict how quickly an adhesive will deteriorate, but the CCI folks think this formulation is likely to show significant change in a decade. The component most likely to change is the tackifier. This means that the qualities that make this snot tape so nice for temporary use, its flexibility and extreme stickiness, are exactly the qualities that it will loose as it ages. Pressure sensitive adhesives are designed in such a way as to increase their tack under pressure. Their traditional use is as thin films used to join relatively light-weight, flat surfaces: labels to paper, card stock to card stock, a nameplate to a wall, etc. They have little shear strength, so cannot be expected to perform well as structural adhesives. This has particular significance in terms of their being used thickly, to secure heavy objects over extended periods of time. Under that type of application, you would expect the heavy object to sink gradually through the soft adhesive, until it is resting directly on the other surface. At that point, there is little adhesive present between the two surfaces and join failure may follow.
The CCI report only talks about the kind of snot tape they analyzed, so what follows is my extrapolation from the information they have given me. The addition of fibreglass will make snot tape stronger and acrylic is more stable than pentaerythritol ester of rosin. So, Scapa 4450 (and similar snot tape formulations) should be stronger than the tape used on Yukon Seasons and may be more stable over time. However, if you have only been using snot tape since 2003, you may not, yet, be seeing how it behaves as an "aged" adhesive. The more stable tapes may loose flexibility and tackiness too, just at a slower rate. Regardless of the formulation, snot tape was not designed for use as a structural adhesive, so lack of shear strength and adhesive migration are likely to be a problem even with the better quality tapes. For this reason, I have recommended we not use snot tape to secure "Yukon Seasons" in the future.
The stability of snot tape is not the only one reason we are currently re-working the way in which Yukon Seasons is secured to its mount. Another factor to consider is the damage to the tip of the moose skull upper palate. Remember that area was abraded, possibly chewed before it was returned? It was the centre resting point for the skull, when the piece sat on its mount. With the tip gone, the skull and mount don't connect correctly. Now the sculpture has just two points of contact: the antler beams. It is free to pivot on them and it does. This is just not safe for the sculpture. The obvious solution is to build up the mount (discreetly) and create a new safe resting point for the skull. Since we have to modify the mount base, we will use the opportunity to modify the uprights so that the antlers sit more securely. Again any modifications we do will be discreet.
The Lock-Out
I've been spending more time trying to re-fit the broken tine. Unfortunately, it's locked out. The broken surfaces of both the detached tine and the main antler are complex, with lots of sharp angles and splintered areas. This will be really helpful when I glue the piece in place, but it is a problem now. All those ridges and angles are keeping the broken surfaces from aligning. It's not that I can't get a perfect fit between the two. I never really expect that with broken organic materials, as they can change shape after a break. The problem here is that the break edges are actually preventing me from placing the detached piece back into the gap left by the break. I can't get the two pieces close enough for a good adhesive bond. There was a great deal of force used to break the tine away from the main antler, but if I try to force the piece back in, I will undoubtedly cause new breaks, including some to carved areas. If I leave the detached piece the way it is, the two parts will only be touching on small points and any repair will be weak and unsightly.
I plan to borrow a method from conservation of wooden artifacts/cabinetry repair. Wooden artifacts suffer from this problem all the time. A conservation solution is to minutely trim the splintered, interior surfaces of the break to allow the detached piece to be re-inserted and aligned. The amount I remove will be tiny and all of it will be taken from those broken, interior surfaces. There will be no alteration of the carved surfaces at all. I plan to use some small plaster rasps, possibly a utility blade for this work. Everything will be done by hand, with extreme care and I will check the re-fit regularly. The goal is to remove just enough to allow the detached piece to slip into place. Then, I will proceed with the repair. Again, I'm not looking for anything like a "perfect" fit here. I'm just ensuring that the broken edges come together for a secure bond.
I've included two images of the lock-out. Note the foam backdrop visible through the gaps between the broken tine and main antler section!
Valery
(moose antler skull carving, moose antler skull sculpture)
The Snot Tape
I asked the folks at the Canadian Conservation Institute in Ottawa about snot tape. I wanted them to comment on its suitability for securing heavy sculptures over the long term. No one has ever asked CCI about snot tape before, but conservators ask them things about art/artifact related materials all the time and they were happy to help. They requested a sample to analyze. Commercial products like snot tape rarely come with a full ingredient list. Analysis helps provide a complete picture of the product, necessary for understanding/predicting its behaviour. I cut a small bit of old snot tape from the Yukon Seasons' mount and sent it to them.
The analysis is done and CCI has sent a report back to me. The results are as follows: the adhesive used to secure Yukon Seasons is a styrene-butadiene rubber with pentaerythritol ester of rosin as a tackifier. There was no evidence of acrylic or fibreglass in the sample. This means that while you may be using Scapa 4450 snot tape now, the stuff you got from the film crew for Yukon Seasons must have been a different brand. Scapa 4450 manufacturing information specifically states that it is acrylic and that it contains fibreglass as a strengthening agent.
According to the CCI report, the ingredients in the Yukon Seasons snot tape are consistent with many commercial pressure-sensitive adhesives. Pressure-sensitive adhesives are designed for temporary use. In this formulation, the tackifier will oxidize readily, losing tack and becoming yellow and brittle over time. It is hard to predict how quickly an adhesive will deteriorate, but the CCI folks think this formulation is likely to show significant change in a decade. The component most likely to change is the tackifier. This means that the qualities that make this snot tape so nice for temporary use, its flexibility and extreme stickiness, are exactly the qualities that it will loose as it ages. Pressure sensitive adhesives are designed in such a way as to increase their tack under pressure. Their traditional use is as thin films used to join relatively light-weight, flat surfaces: labels to paper, card stock to card stock, a nameplate to a wall, etc. They have little shear strength, so cannot be expected to perform well as structural adhesives. This has particular significance in terms of their being used thickly, to secure heavy objects over extended periods of time. Under that type of application, you would expect the heavy object to sink gradually through the soft adhesive, until it is resting directly on the other surface. At that point, there is little adhesive present between the two surfaces and join failure may follow.
The CCI report only talks about the kind of snot tape they analyzed, so what follows is my extrapolation from the information they have given me. The addition of fibreglass will make snot tape stronger and acrylic is more stable than pentaerythritol ester of rosin. So, Scapa 4450 (and similar snot tape formulations) should be stronger than the tape used on Yukon Seasons and may be more stable over time. However, if you have only been using snot tape since 2003, you may not, yet, be seeing how it behaves as an "aged" adhesive. The more stable tapes may loose flexibility and tackiness too, just at a slower rate. Regardless of the formulation, snot tape was not designed for use as a structural adhesive, so lack of shear strength and adhesive migration are likely to be a problem even with the better quality tapes. For this reason, I have recommended we not use snot tape to secure "Yukon Seasons" in the future.
The stability of snot tape is not the only one reason we are currently re-working the way in which Yukon Seasons is secured to its mount. Another factor to consider is the damage to the tip of the moose skull upper palate. Remember that area was abraded, possibly chewed before it was returned? It was the centre resting point for the skull, when the piece sat on its mount. With the tip gone, the skull and mount don't connect correctly. Now the sculpture has just two points of contact: the antler beams. It is free to pivot on them and it does. This is just not safe for the sculpture. The obvious solution is to build up the mount (discreetly) and create a new safe resting point for the skull. Since we have to modify the mount base, we will use the opportunity to modify the uprights so that the antlers sit more securely. Again any modifications we do will be discreet.
The Lock-Out
I've been spending more time trying to re-fit the broken tine. Unfortunately, it's locked out. The broken surfaces of both the detached tine and the main antler are complex, with lots of sharp angles and splintered areas. This will be really helpful when I glue the piece in place, but it is a problem now. All those ridges and angles are keeping the broken surfaces from aligning. It's not that I can't get a perfect fit between the two. I never really expect that with broken organic materials, as they can change shape after a break. The problem here is that the break edges are actually preventing me from placing the detached piece back into the gap left by the break. I can't get the two pieces close enough for a good adhesive bond. There was a great deal of force used to break the tine away from the main antler, but if I try to force the piece back in, I will undoubtedly cause new breaks, including some to carved areas. If I leave the detached piece the way it is, the two parts will only be touching on small points and any repair will be weak and unsightly.
I plan to borrow a method from conservation of wooden artifacts/cabinetry repair. Wooden artifacts suffer from this problem all the time. A conservation solution is to minutely trim the splintered, interior surfaces of the break to allow the detached piece to be re-inserted and aligned. The amount I remove will be tiny and all of it will be taken from those broken, interior surfaces. There will be no alteration of the carved surfaces at all. I plan to use some small plaster rasps, possibly a utility blade for this work. Everything will be done by hand, with extreme care and I will check the re-fit regularly. The goal is to remove just enough to allow the detached piece to slip into place. Then, I will proceed with the repair. Again, I'm not looking for anything like a "perfect" fit here. I'm just ensuring that the broken edges come together for a secure bond.
I've included two images of the lock-out. Note the foam backdrop visible through the gaps between the broken tine and main antler section!
Valery
(moose antler skull carving, moose antler skull sculpture)