Hi there!

Firstly, I love the site and am very excited with the inspirational projects and tips posted here.

I am a long time crafts lover, and tend to focus on clothes and costumes these days, but I recently found myself deciding to make a papier mache mask as part of my most recent costume.  I've done a lot of work so far, but would love some feedback and advice for my next steps. 

So, I made a basic spherical head form around a "punch balloon", and it fits nicely over my head (almost looks like the "Jack in the Box" guy for any western Americans).  In this process I used newspaper and a water and white glue mixture of about 2 parts glue to 1 part water.  It was like watery glue, still pretty thick, I'd say. 

I built this up about 7 layers thick and deflated the balloon, and it is surprisingly rigid when left to stand on its own, and resists pressure, but I suspect this is somewhat helped due to the basic physics of a sphere's structural integrity.  I say this because I then made the mask's "jaw" on the same balloon, but only about 1/4 the area covered, and the jaw piece is significantly more floppy, but still solid.

From here, my plan was to coat the papier mached parts in a few layers of gesso (I specifically am using a watercolor absorbent form) watercolor paints (that's the look I'm going for), and then some form of matte sealant.  I've tested the first two steps on the mask's nose (a third, separate piece), with what seems to be great results, however, the nose was made off of a cardboard base. 

Here is where my concern and questions come in.  While the head base has been sitting around, I have noticed that on humid days it feels just a bit more flexible than usual.  This isn't surprising since it IS just newspaper, white glue (elmers) and water, but I worry about it's strength. 
SO, is there a hardener that you gurus know of that I could apply BEFORE my gesso step to guarantee my dome head and jaw's hardness?  It would need to be workable to take the gesso, and I hope more or less seal the mask.  Also, would such a hardener need to be applied inside as well?  The jaw would be fine since it will sit "outside" of the mask, but I'm afraid of getting light-headed if I'm stuck in a fumey mask.  I guess I hope for something that can "sink in" through the layers.  OR, would the sealant at the end, if I choose the right sealant, be enough to strengthen my mask?  If so, which sealant should I use?

FYI, this mask would never be worn in the rain, but could definitely be worn in a humid summer, which means general humidity, and potentially an especially sweaty me inside of the mask's dome head.  I am afraid of drooping or deformation. 

Sorry for being so verbose, I'm just trying to get as much info to you as possible.  I appreciate any help you can pass on.

Thanks!

-Dan