Frit

Frit support

Frit calculates glaze chemistry from a recipe. This page covers the common questions. If yours isn't here, write to support@barframe.com and say which macOS version you run. A screenshot of the window helps.

The app needs macOS 14 or later. It has no network access, so there is nothing to sign in to and nothing to sync inside the app.

What UMF means

UMF stands for unity molecular formula. The app turns each material weight into moles of oxides, then divides every oxide by the total moles of the flux oxides. The fluxes are Li2O, Na2O, K2O, MgO, CaO, SrO, BaO, ZnO and PbO. After that division the flux column adds up to 1.0, which is the "unity".

The other oxides then read as ratios against that 1.0. Alumina and boron are stabilizers in the app, and silica is the main glass former. A cone 6 glossy glaze often lands near 3 to 4 for SiO2 and 0.3 to 0.4 for Al2O3 against that flux of 1.0, though your clay body, firing and taste decide what works. The numbers describe a recipe. They don't promise a result, so test a tile.

Colorants and opacifiers such as cobalt, iron oxide or tin aren't part of the flux sum. Mark them as additions and they stay out of the formula until you switch on Include additions in chemistry in the recipe view.

How LOI is used

LOI means loss on ignition. Whiting, kaolin and many other materials lose weight as water, carbon dioxide and other gases leave during firing. The weight that reaches the glass is smaller than the weight you put on the scale.

Each material in the app stores its oxide analysis as the fired oxides per 100 g of raw material, with the LOI listed beside it. That is how most data sheets are written, so the LOI is already outside the oxide percentages. The app uses this in two places. The weight percent of a glaze is calculated on the fired oxides, with the LOI removed. And the material editor adds the oxides and the LOI together and shows a note if the total is far from 100 percent, which usually means a typo in one oxide.

If your data sheet gives an analysis that includes the LOI, rescale the oxides to sum to 100 percent minus the LOI before you enter them.

How to add a material

Choose Materials in the sidebar of the glaze book, under Book. The bundled materials are read-only and each shows its source. To change one, choose Duplicate as Custom Material and edit the copy. To start from nothing, switch to the custom list and click Add Material.

Fill in the name, the oxide analysis in weight percent, the LOI and a source, such as a supplier data sheet or a lab report. The source field matters. Six months from now it tells you which sheet the numbers came from. Custom materials are saved inside the glaze book, and recipes that use one update their chemistry when you edit it.

How to export a batch sheet

Select a recipe and click Batch Sheet. Type the batch weight in grams, choose the precision of your scale, and the table shows the grams for each material. The base materials add up to that weight. Additions are scaled by the same factor and weighed on top, marked as additions.

Click Print to send the sheet to a printer, with a tick box beside each material for weighing. Click Export PDF to save it as a file. Rounding to your scale's precision means the total can differ from your target by a gram or two. The sheet shows the real total.

Blends and test tiles

A line blend mixes two recipes in the steps you choose. A triaxial blend takes three corner recipes and makes 15 tiles at 4 divisions or 21 tiles at 5. A four-corner grid fills rows and columns between four recipes. Each tile has a full recipe and a full chemistry. The test log holds the cone, atmosphere, kiln schedule, notes and a photo for every tile you fire.

The Stull chart and limits

The chart plots SiO2 against Al2O3 in UMF, with regions for matte, gloss, semi-matte and underfired glazes. The regions are an approximation of published charts, and real glazes cross the lines. Borders move with the cone, the firing and the other oxides in the glaze.

The limit sets are example reference ranges for cone 6 and cone 10, glossy and matte. A value outside the range is a reason to test, not a fault. The app doesn't judge whether a fired glaze suits tableware. Only a lab test of the fired surface can do that.

Where your files are

A glaze book is a single file with the extension .glazebook. Save it anywhere you can write. Copy the file to back it up.