Preserving chalk pastel artworks?
You will see a dulling or muting of the colors if you use fixative, which is why many pastel artists will actually “fix” in stages. Personally I like to build up muted color layers and use my highlights and whites on the top.

No matter what, you should always apply multiple light layers of fixative, letting them dry in between stages.

Hair spray is good in a pinch (I have used it for decades), but it is never artist grade, as it likely is not pH neutral. Depending on the aromatics and the constituent chemical composition, you may actually (but probably won’t) promote long term damage to the paper.

There is one other notable alternative to acrylic-based spray fixative other than hair spray, but you will need to test them: the “impregnating” sprays used for shoes / leather. 

But if you REALLY want to make it yourself, the classical method would be to dissolve damar varnish flakes in turpentine and use an atomizer.