Glaze Melt Flow - GLFL
NotesThis test is done to evaluate the melt fluidity of glazes. This property is very hard to judge from simple observation on glazed ware or samples. Knowing the melt fluidity of a glaze is very important in maintaining consistency, duplicating and understanding a glaze. This is a simple test that anyone can do, however it does require that you have a special mold to cast flow testers, you can find out about getting one of these in the article linked to this test procedure.
Procedure
1,1
Purpose of Test
This test is designed to measure the fluidity of a ceramic melt (recipe or raw material) and achieve the thick melt body necessary for making objective repeatable visual comparisons. While not absolute, it is valuable to compare the melt patterns of two materials and subtle color and character differences in translucents and transparents.
While it is possible to compare melt flow, color, etc using standard glazed specimens, this approach has serious draw backs.
-It is very difficult to achieve the consistent application thickness that is critical to the amount of flow and the intensity of color in non-opacified melts. The intensity of transparent colored melts (i.e. iron containing glazes or clays) are dramatically influenced by even small thickness variations. The intensity of bubble, speck, and crystal development are also highly affected by glaze thickness. Making visual judgement comparisons is thus difficult using traditional glazed specimens.
-Certain plastic and non-plastic materials do not lend themselves to application as a glaze, they do not adhere or flake off as a result of high shrinkage. These work with no trouble in a flow tester.
-The relation of glaze-flow to thickness of application is not arithmetic. Glazes that seem stable when applied thinly can run dramatically when thicker. For glazed specimens to have any value as flow indicators the application has to be so thick that adhesion is often compromised during drying and there are runoff problems. Runoff in a flow tester can be quantified and recorded easily.
-Flow testing is best carried out inclined rather than vertical surfaces. This allows for the achievment of a much thicker melt body, an important factor in visual comparisons. Thin transparent glazes, for example, can appear very clear but when these are put into a flow tester iron content will display itself immediately as a distinctive amber color in the glass.
Plainsman Clays uses this test from cone 8-10 to compare the flow of different runs of Alberta Slip, with each other, and with Albany Slip. In addition, glaze recipes employing an Alberta Slip:Frit mix are flow tested to provide a more sensitive comparison test for color and speckle.
This is also used to compare Ulexite, CadyCal and Boraq batches. For Ulexite use Cone 08, Cadycal cone 05, and Boraq cone 06.
It is important to adapt an optimum temperature for each material or recipe type being evaluated. This temperature should be a compromise between good flow and enough stability to maintain a good melt body on the runway.
2.1
Scope
Tests are prepared as needed to compare with a reference material or to simply compare fusibility, color, speck development.
3.1
Definitions
QC - Quality Control Department
4.1
Responsibilities
Done by QC.
5.1
Procedure
5.1. Process the Specimen
5.1.1. Mix the powdered material with water and prepare a thick paste that can be formed into a small ball. If the paste is too thick, dewater it on a plaster batt.
5.1.2. Form small balls about 2 cm in diameter. Let them dry.
5.1.3. When the balls are dry, sand or shave them down to 13 grams in weight.
5.1.4. Place balls from the two materials to be compared in a standard IMC flow testing device. Write the identity (using a ceramic pencil) beside the reservior of each.
5.1.5. Fire the device in the lean-back position to the desired temperature and compare. Make appropriate notes about the character and length of the flow and enter the cm length of the flow in the test records.
5.2. Equipment
5.2.1. Flow testing devices. There is an article and photo in the Magic of Fire II. The runway should be 85mm long and at a 40 degree angle to the base. The reservoirs are rounded to about 1.25 cm radius and have a lower flow opening of 5mm from the base tapering to 1.2cm at a point 2cm up.
5.2.2. Mixing equipment to prepare plastic sample for modelling balls.
5.2.3. Kiln.
5.3. Safety
5.3.1. Do not breathe clay dust unnecessarily.
5.4. Workmanship
5.4.1. Be careful to get a representative sample of the powder.
5.4.2. Weigh the balls carefully to make sure they are the same weight. Be sure they are dry when weighing.
5.4.3. Do not fire the kiln too fast to avoid excessive boiling of the melt.
5.4.4 Do tests at several temperatures to get a complete picture of the melting behavior of the material.
5.4.5 Use a white burning non-refractory clay to act as a neutral background on which to make objective visual comparisons. 50% ball clay, 25 flint, 25 feldspar is a good starting point as it does develop some maturity at cone 6-10 and therefore does not interact excessively with the melt being tested.
Variables
LEN - Length (V)
Suggested units are cm
NOTE - Note (V)
Characterize the flow noting bubbling, blistering, matting, crawling, etc.
Out Bound Links
In Bound Links
Pictures
Flow tester used to compare feldspars
G1215U vs. G1215W glaze flow test
Flow tester comparing the melt fluidity of Albany Slip vs. Alberta Slip at cone 10R
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