Yikes! Nothing but clear stuff coming from the tube! There are two reasons that the pigment separates from the binder medium and the polymer emulsion in which it is suspended in the paint tube – age, and changes in temperature. Living in Australia, I sometimes drive for days to reach workshop destinations, and the art materials in my car go through wide changes in temperature so such separation is not rare for me to experience. Certain pigments are heavy, and more likely to separate from the acrylic resins, such as the Pyrrole Red in the photo below and many earth colours.
Put the tube (with the lid back on!) into a sock or cloth bag and swing it around with gusto. Count out at least a minute for the time to do this, and almost magically, the paint will be all together again. If this doesn’t work (usually due to age) squeeze all the tube contents out into a small jar with an airtight screw lid, mix with a clean dry palette knife and label, as I have done with the Naples Yellow in the photo above.
Such separation is a sign that the paint is of a high artist quality containing real pigment. So put a sock in it! Your art kit I mean – keeping a sock in with your paint tubes may come in handy. There is more information in my book “Using Chroma Art Materials – Tips and Techniques for Creating Art” available for purchase from the home page on my web site triciareust.com.au.