I am writing to ask for help in solving a problem. I am currently doing open faced relief sculptures, some of which are showing a haziness upon the glass that is in contact with the mold itself. I am following the bullseye method with certain deviations (using silicone or wax positives). I am cleaning the glass using the bullseye method. I am using 001841-0065 Spruce Green Billet. The works are placed in my kiln on stainless steel bowl full of sand.
I have air dried the mold for a month and then placed the empty mold in my kiln at 200f for 8hrs. Then, after weighing and cleaning the glass, i place the glass in the mold and fire at the following schedule:
1: 100f - 200f - 4:00hrs
2: 100f - 1250f - 2:00hrs
3: 600f - 1525f - 1:30hrs
4: 9999f - 900f - 4:00hrs
5: 7f - 800f - 0:00hrs
6: 12f - 700 - 0:00hrs
7: 41f - 70f - 0:00hrs
I have included two images. The first (IMG1.jpg), shows a successful cast, there is not haziness on the surface - the surface only reflects the surface texture of the original positive. This particular mold came from a wax positive that was steamed out. I have also produced successful molds using a silcone positive, in which the two-layered investment was created over the silicone positive.
The second image (IMG2.jpg), shows signs of a scummy like haziness. I will say at this point that there are no signs of devitrification on the back of either of these work, only a scum on the surface that was in contact with the mold.
I am, essentially, seeking to eliminate whatever is causing this problem. So far i have excluded the following:
1) It is not the glass cleaning, as i am meticulous about this, and again, the is little to no devitrification on the back - and i am told that the open surface is where devit will usually appear
2) It is not the material that i make my positive with as i have has sucess with both steamed-out wax and a peeled out silicone positive
3) It is not the firing schedule as i have had numerous successes with the above schedule
4) I have been using un-distilled water the entire time, and again, have had numerous sucesses- so it is not that
5) I have thoroughly vacuumed the surfaces of my molds before placing glass billet in them - so it is not that
6) It is not the stainless steel bowl as again, i have had success using it numerous times.
My only thoughts are:
1) The investment material might not be mixed properly
2) The investment material might be old
If you look at IMG2.JPG you will see 'water' like movements of this haziness upon the surface, which leads me to think this is either from the glass flowing over the mold OR that this inconsistency has actually come from when i applied the investments to my original positive.
What is also frustrating is that my "failed" mold (ones which show this scuzz or haziness) have patches of being "clear" like my successful mold. If you look at IMG3.jpg i have drawn a red arrow pointing to an area on the glass that seems unaffected by this scuzz.
If you have read this far, thanks - and again, i'm kind of at a loss, any help would be appreciated.