This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
The amount of oil that can be permanently emulsified varies with the emulsifier, the oil used, and the manner in which it is added. Pickering has emulsified "99 per cent of paraffin oil in 1 cc. of 1 per cent potash solution by successive addition of small portions." The concentration of oil in food emulsions varies from a very low percentage up to about 85 per cent.
Mayonnaise containing slightly more than 95 per cent of oil has been made in the laboratory, but it usually breaks shortly after a little more than 90 per cent of oil has been added. The stiffening of mayonnaise containing over 90 per cent of oil makes it difficult to mix the last addition of oil. Mayonnaise with more than 90 per cent of oil resembles jelly in consistency; cut with a knife or spoon it retains its shape. It will keep varying lengths of time in a covered jar in the refrigerator. Some break in a short time, but most of them keep for several days or weeks. Probably this variation in breaking is partially due to variations in beating in forming emulsions. After standing a short time, if the dressing is cut or if some is lifted out of the jar, there is a tendency for oil drops to form gradually on the cut surface. It separates more readily than mayonnaise with a lower percentage of oil. Ordinary mayonnaise containing from 1/2 to 3/4 cup of oil to 1 egg yolk and 15 cc. of vinegar averages from 65 to 75 per cent of oil. Hall and Halstrom, by introducing the oil beneath the surface of the forming emulsion, obtained mayonnaise with a concentration of 89 to 93 per cent of oil that remained stable for two years when stored at 8°C.