You might also want to check out a few pages at my site for info about doing both those things in various ways:http://glassattic.com/polymer/finishes.htm
(click on > Varathane >> General Info
, then scroll down to paragraph called "Making Gloss Varathane NOT-Shiny" though should work for most any clear water-based finish too)
Here's some of what's suggested there:
(Going over a piece with matte glaze can look cloudy and thick.)
Some light abrasives that can be used to take down glossiness are:
...very high grit wet-dry sandpaper (1200 or higher)
...light pumice powder (hardware store)
...0000 steel wool
Or before baking, other fine abrasives can be used like cornstarch, Bon Ami or on very fine sandpaper, and more. And one person recommends "finger-polishing raw clay with water, then using no varnish at all after baking."
Another idea is just to "texture" the raw clay with a very-fine material of some kind (high-grit sandpaper?, pouncing repeatedly with an emery board or fabric, etc); those things will physically and visually break up the smoothness of the surface so it can't look shiny.
After any of those (after baking), can then be lightly buffed by hand if you want a less
dusty-lightish look (...and don't reheat the clay since that can partly melt the surface clay back to a smoother appearance). Or leave as is.
If the item is highly dimensional, that could leave a more glossy look in the lower areas after dulling the upper areas (if not using a fine tool or toothbrush/etc. to get down into those areas), so if necessary you could later "antique" those areas with a matte acrylic paint (artists' tube paints work best) like dark brown, or even mix a bit of very fine powdery material (even dirt) into it to make those areas grubbier looking**. Other colorants can be used down in the crevices instead too.
If you don't know about "antiquing," check out at least this page at my site:http://glassattic.com/polymer/molds.htm
(click on Antiquing, Highlighting, Staining
("Backfilling" on the Carving page would be another possibility, but perhaps more stuff in the lower areas than you'd want.)
If you really want to make something look old-old in particular, also check out this page:http://glassattic.com/polymer/Faux--many.htm
....click on Ancient and Aged Looks
That page also has lots of other materials that can easily be simulated with polymer clay so if the material/item you're making is one of those, you might get more tips from those categories as well. (There are a few other materials with their own pages too, like faux wood, faux ivory, and faux turquoise.)
** "inclusions" of all kinds can be mixed into polymer clay, or into liquids like paints, clear finishes, etc (e.g., dirt, ground spices and herbs, and more):http://glassattic.com/polymer/inclusions.htm