As a cosmetic formulator you will undoubtedly run into a situation where you screw up a batch. Or maybe the batch just gets ruined through no fault of your own. Most of the time you should simply throw the batch away and start over.
Of course, I am speaking from the point of view of a cosmetic chemist who worked for a large corporation and usually had access to a nearly unlimited supply of most of the raw materials I was working with. The only negative thing about pitching most batches was the extra time required to make a new one. But for most cosmetic formulators pitching a product and starting over is a luxury and saving every batch is important. So, here are some tricks I’ve used (for the times I couldn’t discard a batch) to save a batch.
When is a cosmetic batch bad?
Before we give tips on saving batches, it makes sense to consider how to decide whether the batch is really bad. Since every cosmetic formula should have a set of specifications these can be used. If a value such as the pH, viscosity, color, odor or consistency is “out of spec” then the batch is considered bad. While this does not guarantee that every in-spec batch is good, it is a reasonable filter for most cosmetic chemists to follow. The other way a batch can be considered bad is that it doesn’t perform the way it’s expected but that is a much more complicated situation which we will ignore for this post.
Figure out why it went bad
Once you’ve decided a batch is bad, you should figure out what went wrong. This will depend on which characteristic is out of spec. For example, if the pH is too low maybe you added too much acid or not enough base. If the color is off perhaps the wrong amount of dye was added or one of your starting raw materials was a different color than usual. Go through your batch notes and identify what the possible problem could have been. Sometimes you just can’t know but it does make fixing things easier.
How to save a bad batch
Here are some tips and tricks on how to save a cosmetic batch. The specific tactic you use depends highly on the type of formulation you are making.
Remix & Reheat
If your product is thin or has the wrong consistency one of the first things you can try is to reheat the product and mix it again. Often an emulsion won’t form properly during the cooling phase and remixing at a high temperature can reset and fix things. If you do try this however, be sure to add back more of your heat-sensitive ingredients like preservatives and fragrances as these can breakdown when heated for a significant period of time.
Add more of the missing ingredient
When you notice an obvious error in the amount of an ingredient, you can often add more of the ingredient at the end of the batch to make things come out properly. This usually only works with liquid raw materials.
Add adjustment ingredients
If the pH is off you can add ingredients like acids or bases at the end to get the batch in spec. This is where doing something like a formulation knockout experiment is extremely helpful. By doing a knockout experiment you can determine the effect that every ingredient will have on the end characteristics of your formula. Some of the ingredients will have a significant effect on thickness or pH even if you wouldn’t expect them to.
Dilute with a new batch
Sometimes you can’t adjust a batch for a variety of reasons such as adding 10 times too much dye. In those cases, you can make a second batch where you leave out the color and then blend the two batches together to make one that is the correct color. This can work for pH and viscosity too. However, you should know that while this technique can lead to a fixed batch, it can also lead to two broken batches! So, use it with caution. There were times when we would have to dilute a production batch over months and many other batches just to save it.
Sometimes you have to throw things away.
While there are often ways to fix batches, there are times when things are a lost cause and you should pitch the product. For example if your batch is microbial contaminated you should not use it. Granted you can do things to kill off any contamination but certainly on a lab scale it is more safe to just discard these batches. Remember the time and effort required to save a batch is sometimes not worth it.
Do you have any batch-saving tips or questions? Leave a comment below.
April is Focus on Formulation month. All month long the majority of blog posts will be about cosmetic formulating.