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Preserving Petrified Wood
Submitted by admin on Tue, 10/26/2010 - 03:14
To have the greatest possible beauty in petrified wood is a special reward which comes with a bit of special effort. The fractures and open cracks which are natural, especially in full rounds of medium to large size, requires special treatment to prevent further breaking. To permanently preserve a specimen will produce the needed results.
- Place cross section "round" in cold oven. Set temperature at 225 degrees. Heat until the entire piece is that warm. This may require several hours, depending on size.
- Remove from the oven. Using a very narrow metal spatula or rod put Opicon 224 Fracture Sealer only along the fracture on the top side of the stone. The heat of the rock causes the Opticon to be absorbed quickly. Repeat this until all the cracks are filled. It is necessary to have the first application drawn into the rock because this is the strengthening, stabilizing seal. Avoid letting any Opticon get into large holes, which would give the finish a filled appearance. Leave the holes as natural holes.
- Repeat this process on the reverse side where one need not use as much detail care. On large pieces with major cracks to repair, brush a thin layer of Opticon over the surface to within about one-half inch from the edge. Keep the narrow border absolutely clean and clear. There must be no evidence of sealant on the outer edge or rim of the specimen. Over this thin layer of Opticon, place a layer of fiberglass which you have precut to proper shape. Cover the fiberglass with another layer of Opticon, brushing the sealant on and making sure that all threads of the fiberglass are saturated. Here again, be very careful not to let any sealant on or drip over the edge of the rock. The natural outer surface of the specimen must be retained and Opticon just cannot be removed without scarring that surface.
- Put the piece back in the oven and let cool for several hours.
- Polish the flat surface to the natural edge. My procedure is with a high speed sander with a 7" disk in horizontal position. This means that the piece must be a size that I can hold up to the sander. I enjoy seeing the polished surface developing with the hands on process. The sander running at 3400 rpm, I use 36,100,220 and 320 grit sandpaper. For the final polish, I use cerium oxide on a leather buffer.
- A flat lap is the machine to use when polishing large rounds. 1 use 220,400, and 600 grit. For the final polish change the lap plate to one covered with indoor/outdoor carpet or felt. Apply cerium oxide and stand by, keeping the surface moist but not wet (the same principle as polishing a cab). Time required is dependent largely upon size and quality of the specimen.
A piece permanently sealed and with a well done surface revealing the unique features of the specimen is a real beauty to appreciate and for everyone to enjoy.
Bill Hall, Contributing Author Oregon Rockhound Bulletiin/Feb. 2008