There is a lot of use of powdered glass in a medium supplied in an applicator bottle. This is convenient and expensive. You can approach the consistency of the commercial product by use of CMC
CMC is carbyl methyl cellulose. It is a binder (glue) and it helps keep solids suspended in liquid. You can buy it at a pottery supplier as it is often used in glaze mixtures and known as a glaze binder. It is also used a lot in the food processing industry and is available as food grade CMC. It normally is supplied in powder form.
To make use of it you need to dissolve a teaspoon or two in a half pint of water and let it stand. It does take a while to wet and in doing so it expands. By the next day it will be a thick mass. It can be further diluted, but it is often best to make it to the consistency you will need for the current purpose. It will require a little experimentation to get the proportions right for various purposes.
Put on a dust mask. Sift the powdered glass to remove the coarsest particles and mix the result with the CMC, 1 to 2 of powder or more. Mix thoroughly and leave to stand overnight. Then dilute to the desired flow if required and mix well. Again let it stand overnight to completely incorporate the powder. If it is too liquid, it is desirable to add more powder than more CMC to avoid diluting the colour.