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The Hemisphere Paperweight Project*

Description: We will be creating a fused glass paperweight using a ceramic, hemispheric (1/2 a ball) mold using purchased and handmade frit and cullet. The pieces will be full fused, cold worked and fire polished. Annealing will be introduced both during the firing and fire polishing stages.

 

Materials needed: Hemisphere mold, Frit, fusible glass, cullet, dichroic glass if desired, kiln wash, a grinder, high fire wire to support the mold, kiln shelves, patience and time.

 

Process:
  • Wrap the mold with high fire wire, tying off through the hold at the side. Wrap wire at least twice around the circumference of mold. This adds additional support should the mold crack during firing to ensure that molten glass does not flow onto the floor of your kiln. Molds do crack from time to time through normal use and aging.
  • Kiln wash the inside of the mold; be sure you use an even coating because any irregularities in the kiln wash will appear as texture on your piece. You may smooth the kiln wash when dry with your fingers or sand paper but be sure not to remove in anywhere or you piece will stick and crack. Let the kiln wash dry 100% before proceeding. Make sure the little air hole at the bottom of the mold is not filled with kiln wash. This is to allow air to escape so you donít get bubbles in your piece. Just use a pin to carefully open the hold from the inside of the mold. Take care not to chip away kiln wash on the inside of the mold or your piece will stick and crack.
  • Gather your frit, cullet and any other glass you plan to use. You can make the pieces of cullet smaller and make frit from sheet glass by placing it in a cloth, placing it on a VERY hard surface like cement, and hitting it with a hammer. Make sure you wear protective eyewear as stray pieces may escape during vigorous hammering. Bullseye recommends scoring the back of the cullet and then tapping on the opposite side of the score line, much as you would to encourage any difficult break but I have not found this to be easy nor effective. Maybe youíll have better luck.
  • Fill the mold with your glass as desired. Keep in mind that the bottom of the mold will be the top of your piece. If using dichroic glass with a transparent frit/cullet make sure you layer it between frit layers to add depth. Fill the mold so that there is a cone of frit built up from the middle. SEE PHOTO.

 

 

  • Firing your piece: Youíll see in the photo that Iíve covered the bottom of the kiln and gone about 1" up the sides with fiber paper. This is a precaution against molten glass coming out of the mold and isnít really necessary but is a paranoids safety measure which you may want to employ. Itís up to you. I use pre-used fiber paper as it is softer and easier to press into the shape of the bottom of the mold but I donít pre-use it specially for this; I would use new fiber paper if I didnít have used stuff around already. Be pratical!

 

Place your piece in the kiln as shown in the photo. Donít rest any part of the piece against the thermocouple (the rod sticking out of the back or side of your kiln). Close the door tightly and set the kiln to fire to full fuse. You can fire these pieces fast the first time because they are not solid but are frit. Youíll see when fire polishing we need to be much more careful as they will be one big solid piece of glass. I fire this in an older Paragon SC2 at Speed 4 which is 1000 degrees per hour until it reaches 1490 degrees. In the newer SC2ís this is to 1540 degrees for a full fuse. I soak it at the full fuse temp for 15 minutes. You will have to play with this to find the optimal fusing temp and soak time for your kiln. If you underfire youíll find that the flat Ďtopí of the piece is not smooth. It should be as smooth as ... well... glass. We will not add time for annealing here as we will do that during fire polishing.

 

When the kiln is under 200 degrees you may remove your piece. Let it sit outside the kiln until it reaches room temp before removing it from the mold. DO NOT WASH IT OFF TILL THE NEXT DAY. DO NOT FIRE POLISH TILL THE DAY AFTER FUSING.

DO NOT PEEK. DO NOT CRASH COOL. DO NOT OPEN THE KILN UNTIL THE TEMP IS 200 DEGREES OR BELOW. BE PATIENT OR YOUR PIECE WILL CRACK.

 

  • Cold Work: Once your piece is FULLY cooled you can take it out of the kiln and out of the mold. Be careful as there may be what we call in Maine Ďpickedsí around the flat edge; these are really really sharp little pointy shards of glass. These must be ground off. This can be done with any glass grinding tool but the most commonly found grinder in the average studio is the Inland or Glastar type grinder with a diamond grinder bit. Run the edge of the piece round and round till you have a nice smooth edge. You should wait one full day before wetting the piece to make sure it is cool all the way through and prevent thermal shock cracking.

Wash the piece off, dry fully. Make sure there are no finger prints on the piece. Hold the piece by the edges to limit fingerprint transfer. Wear cotton gloves if this is a problem for you. Some people recommend using alcohol, glass cleaner, soap etc.... to clean the glass. I do not. I recommend using nice clean warm water and your fingers. Chemicals can leave a residue that will react when fired causing all sorts of weird things to happen to your piece; none of them pleasant or desirable. Wipe the piece dry with a paper towel to prevent water spots.

 

  • Fire Polishing: Because this piece is thick we need to proceed with caution. Firing too rapidly will cause your piece to crack. It is better to err on the side of caution! Place your piece into the kiln on a prepared kiln shelf. Using the SC2, I fire at Speed 2 or 200 degrees per hour to 1365 and hold for 10 minutes, then lower the temp as fast as possible to 960 and hold for 4 hours to anneal, then allow the kiln to cool to room temperature as fast as possible. This will take several hours.

DO NOT PEEK. DO NOT CRASH COOL. DO NOT OPEN THE KILN UNTIL THE TEMP IS 200 DEGREES OR BELOW. BE PATIENT OR YOUR PIECE WILL CRACK.

 

TROUBLESHOOTING:
  1. Your piece is not smooth: You did not fire polish long enough or to a high enough temp.
  2. The bottom of the piece (which is the top when in the kiln) is bumpy: You need to fire hotter or longer.
  3. Your piece is no longer a hemisphere but has flattened out to some degree: You fire polished too long or to too high a temp.
  4. Your piece cracked after taking out of the kiln: You took it out of the kiln too soon (or you peeked) and it was thermal shocked. This is from room temperature to 1000 degrees. Lower your ramp speed. You can pop the pieces back in the mold and re-fuse.
  5. Your piece cracked in the kiln:
    1. If it is an ĎSí shaped crack, you heated too quickly; if the crack radiates in all directions from a single point then the kiln wash was not applied to the center of that center point. You can pop the pieces back in the mold and re-fuse.
    2. Did you have metal inclusions? If so, you need to do the initial heating more slowly as the metal will heat more quickly. Fire to 350 degrees and hold for 10 minutes then heat up to full fuse as normal.
    3. Perhaps you cooled the piece too quickly. From 1000 degrees downward Ė DO NOT OPEN THE KILN until it reaches between 200 and room temp.
    4. The crack follows along the line where two colors meet up: the two touching pieces are not compatible.

 

  1. Unwanted Bubbles: Are caused by heating too quickly between 1300 and final fusing temp. Fire more slowly thru this stage to allow air to escape. Make sure the hole in the bottom of the mold is open or it can trap air and form an ugly bubble at the top of your piece. The smaller the pieces used, the more air bubbles you will have.
  2. Kiln wash sticking to the surface: the brand of kiln wash you use is important.  The kind we sell works. We don't pre-fire out kiln wash but allow it to air dry. Let the piece cool for 24 hours, then soak it in water and use the scrubby part of a kitchen sponge to clean off the kiln wash. NOTE: I have found that opaque, pastel colors stick to kiln wash no matter what! Colors like white, opaque yellow or pink.....
 

 

Finished Paperweight: Top View

Transparent Turquoise glass w/ embedded dichroic

 

*Same process can be used for the stainless square paperweight mold.

 

 
 
 
 

Updated 3/2/05.

 

 

 

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