This is a piece of borosilicate glass that is used in the construction of the mirrors that are made by the Steward Mirror Lab. This glass and thousands like it will be melted in a huge furnace and spun-cast for days until the ghost of a new mirror is formed. Later, it will be ground to the perfect parabolic shape needed to reflect the light of countless stars. About 20.5 tons of glass went into the casting of the 8.4 meter mirrors for the Large Binocular Telescope.
Pieces of a ceramic material are
used in the formation of the honeycomb mirrors made at the lab.
Each piece of ceramic is uniquely shaped so that the pieces will
fit perfectly into the rough shape of the mirror. Holes in the
sides are where fasteners are placed. This mold assembly will
be covered with the borosilicate glass and baked until the glass
melts. The ceramic will then be removed from the mirror producing
a light weight piece of glass from which the mirror will be ground.
Side view of mirror blank showing the honeycombed effect when the ceramic molds have been removed from the glass of the mirror. These pieces of ceramic would be removed with the mirror standing on its edge. Imagine a multi-ton piece of glass standing on its side towering 8 meters above the worker.
After the ceramic framework of the mirror has been constructed and the borosilicate glass has been added, the entire structure of the mirror-to-be is placed into a furnace and baked. The structure is rotated slowly for the entire heating process and the liquefying glass fills the cracks within the structure. Computers monitor the entire process which takes several weeks to heat, melt and cool. The blue structures visible in this image hold the structure together as the glass expands with the heat.
This is a nearly finished 8 meter primary mirror blank waiting to be ground and polished. The long process of grinding and polishing can take as long as 6 months. This is actually the bottom of the mirror.
Close up detail showing the edge of the mirror's surface. The edge of the glass is only about an inch thick. This image also shows the detail of the honeycomb shapes produced by the ceramic blanks that made up the basic shape of the mirror.
This is a closeup of the mirror as it rests on what will eventually be the reflective surface. The supports seen in this image adhere to the mirror's surface with no more than bathroom caulk between them and the glass. This surface will eventually be ground to a parabolic shape.
This is the auto actuated pitch lap machine that is used to polish the mirror's surface. The pitch lap is computer controlled to remove glass to the perfect depth so that the parabolic shape of the mirror is produced. This slow process takes weeks with daily holographic images taken to insure a smooth surface.
As the mirror's surface is ground and polished to perfection, tiny bubbles within the glass may surface. Since these bubbles would produce pits when they ground open, workers lying on foam mats and armed with flashlights must inspect the surface daily to look for these pockmarks. These holes will be filled with compound and ground smooth with the glass' surface by the grinding machine.
Close-up image of a job hard on the knees and elbows. These workers worked carefully and wore no shoes on their feet. Only socks. They also double checked each other's work, inspecting areas already covered by another man.
Image showing the circles where bubbles are being revealed at the surface through the grinding process. After the mirror has been ground to shape it will continue on to be aluminized and transported to its observatory.
