A tangential note: Thymol should be considered an unnecessary ingredient for almost all emulsions we're likely to make and use. It's a preservative, and basically a carry-over from the days before reliable refrigeration and when gelatin was more likely to be contaminated with odd bacteria. If you make small, frequent batches of emulsion and use them within a week or two, you won't need a preservative. I strongly recommend this for two reasons.

1) Making good emulsions is all about practice, practice, practice. If you make up big batches, infrequently, you'll likely never learn the 'tricks', which are nothing more than the application of experienced observation.

2) The characteristic curve of an emulsion gradually changes during long storage, preserved or not. Any attempts at standardizing to a contrast grade will be made much harder unless you also standardize to a pre-coating storage time range.