Jamie Hascall 4/21/14
I've recently come across an interesting moldable silicone putty and have done a couple of trials to see if it can be used in a way similar to epoxy putties (Pliacre). Sugru ( http://sugru.com) works like a somewhat brittle clay with very little tendency to slump and strong adhesion to most substrates. Working time is about 30 minutes at 70° F and full cure takes 24 hours. Cured Sugru is relatively hard with a durometer of Shore 70. I used it as a test lining for a mount grip to see how well it conformed to surface detail when used with a saran-wrap barrier. The overall product seemed easy to use and the conformity was very acceptable. The silicone is fairly rigid, but not nearly as hard as cured epoxy. It is not grippy like a two part silicone tends to be. It can be trimmed with a razor knife. The cured pad of material seems to lock into the surface irregularities of the object well and give a nice hold. The one drawback I have found is that there seems to be a small amount of residual silicone on the cured surface that you can feel when you handle it. I cleaned it with Ethanol and found that most of it seemed to go away. My question to the group is this. Does anyone have a method or protocol for testing the cleaned surface to see if there will be an unacceptable amount of residual silicone that may transfer to an object? My gut feeling is that it should pass an Oddy Test, but I'd love to see what institutions with sophisticated testing equipment might find as other positive and negative aspects to this material. I look forward to others trying this product and discussing their results. Jamie Hascall Independent Mountmaking Consultant Seattle, WA
Sounds like an interesting product, I'll have to check it out.
One thing you might look at is leaching of oils, which can be a problem with silicones. An easy test we've used before is to get a unglazed terracotta planting pot and clamp a sample of the material to it. If there is any migration, you'll see it on the pot.
(BJ Farrar, Mountmaker, Antiquities Conservation, Getty Museum, Los Angeles, CA)
Here is a somewhat dated but interesting paper on Silicone Rubber Staining of Terracotta Surfaces.
Philip Brutz Mount Maker Exhibition Production The Cleveland Museum of Art 11150 East Boulevard Cleveland, Ohio 44106-1797
T 216-707-2617 F 216-707-6687
Jamie Hascall 4/21/14
Thanks to both BJ and Philip. The unglazed terra cotta is a perfect test surface for detecting both present and ongoing silicone migration. I'll set up a group of test samples cleaned in various ways and uncleaned controls. The article cited by Philip is a little different situation as it was in regards to casting molds of terra cotta objects with silicone compounds. The article was documenting staining from the silicone which was in contact with the terra cotta object while it was curing. In the use I envision for the Sugru material, there would be no contact with the object during curing, and the cured material would be cleaned before actual contact would occur. The two real questions then involve whether the cured silicone can be adequately cleaned of residual silicone oils, and whether there may be un-reacted fractions of the original compounds that will continue to migrate to the surface. I'll try to bring along the test samples to next month's Mountmaking Forum in Santa Fe. I Hope to see you all there. Jamie