Check the pH . Oil tends to emulsify with water at high pH while oil/water emulsions tend to separate at low pH . I'm not familiar with the bluing process . Is the bluing agent acidic ?

Bluing agent is a Salt (alkali)

SAMP,

The processes you are explaining as phosphate and bluing are not clear enough to conceive. However you may assess the problem based on the following guidelines.

*Emulsions are sensitive to electrolytes, extreme pH values like acidity/ alkalinity. The best thing you can do is to go for a compatibility test based on various emulsifiers and pH based choice and not a common emulsion for both.

*The preparation care- like speed of stirring, oil and water ratios , choice of emulsifier and it's percentage are to assessed.

*Emulsions can break in case of elevated temperatures, pH conditions, ionic incompatibilities imposed by electrolytes.

*Try non ionic and anionic emulsifiers and confirm specific use.