How to preserve 'water color'/ 'Pastel color' paintings?

Matting and framing is the best way for watercolors, pastels should be 'fixed' with an ARTIST GRADE ( other grades tend to break down or yellow over time, and you DON'T want that) fixative (or fixatif) . It's a bit more than anything you can buy at the dime store but well worth it. Just hold the can about a foot away from the pastel (or whatever the can says...listen to the can!) and gently sweep in across the paper for even coverage. I've been doing this for years.

Any spray will dull the colours. I would never use a spray on a watercolour. It doesn't DO anything except make the colours dull. For a soft pastel painting you might need to 'fix' these with a spray. Be prepared to lose some of the work's brightness. Framing them behind glass is the best protection.

Both will benefit from being matted and framed in acid-free, archival quality materials. This keeps the "original painting" from contacting any surface that might discolor it. Pastels also require spacers so that they are protected from contact on the surface which might damage the delicate pigment particles. Never spray either with any kind of fixative if you value the original colors! Watercolor only need be protected from moisture and light, and pastel particles, which give it sparkle and luminence, will be fused by fixative, and the glow will be diminished. I work in pastels and rarely, RARELY use any kind of fixative. I find it dulls the colors, and eliminates the characteristic radiance of pastels.

First step is to rush out and buy a protective spray. I would recommend Clear Gloss Spray by Craft Gallery. It protects and finishes the work. It also drys quickly so you don't have to worry about your work being damaged being left outside for long to dry. Also it is great for charcoal works and even acrylics...It gives you a great finish. I use it on all of my works. You can purchase 400g aerosol can for only around $5 from your local dollars and sense or somewhere like that. You can buy it from places like Art Riot too but they charge double the price.