Hello Dopapier, well the vase needs to be able to be drawn on with paint and pens etc... and so probably needs to be able to withstand quite a lot of pressure... It won't need to be fully waterproof and will not serve the function of a vase but will need to be quite sturdy as lots of people are going to be decorating it. I don't really have much experience at all but am willing to try lots of different materials and techniques!
Thank you for your reply! Ella

Here's my suggestion ... (and I reserve the right to submit another -- this is the just the first one that occurred to me.) 

(having just written it out below, I'll first suggest that you do a trial run of the technique using a toilet paper tube, just to get a feel for how it all works) ...

I'd suggest getting a cardboard concrete form cylinder (sonotube is one brand) ... you can get them at big box building supply stores like home depot and lowes ... they run around $6-10, and are between 8"-12" in diameter.  Pick the size you want.   

Lay the tube down on some paper, and mark the side edge of the tube.  Then determine the profile shape you want (where it curves and how much, and draw that as well.   This will give you a template of the profile that you can transfer to cardboard. 

Cut out a bunch of these templates.  (for an 8" diameter tube I'd suggest cutting 8 ... but play with it and see.)  These can be from a single large piece of cardboard or several (make friends as big box stores because you'll want some of their literally big boxes).  The templates (or profile boards) will be inside the mache, so no one will see if you had to join several pieces of cardboard to get the sides 5' high.

(Hot) glue the cardboard pieces at regular intervals around the outside of the cardboard tube. 

Now you have a couple of options.  You can stuff the spaces with crumpled paper up to the edges of the cardboard profile templates, tape them down and then strip mache over this.  Or, what I do, is use strips of cereal box cardboard glued down to the edges of the templates, and then tape and mache over this.  It makes a sturdier surface.

This way you'll have the vase looking pretty close to the shape you want before you start macheing.  Also, since it's so big, you'll likely macheing large strips (like whole or half newspaper sheets) ... so the macheing should go a bit faster than if using very small strips.  Do 4-5 layers and it'll also be very sturdy. 

Good luck!  Let us know how it goes.

Here's another suggestion... I saw this being done many years ago when I was taking an evening art class. 

Someone in another room was making a vase using a large inflatable vinyl beach ball that was sitting on the top of a large bowl or wastebasket, and top of the ball had a  cardboard collar (like a wide funnel) sitting on the top.  The bottom of the wastebasket sat on an upside down bowl for the vase base.  All the pieces were taped together with what looked like masking tape.

I never saw it again, and I am assuming that they covered it with several layers of PM laminate.  They might have also wrapped the entire form in plastic for easy removal of the objects.  If you wanted to save the ball, be sure to place the inflation part where you could get to it easily as you dismantled it.

Of course, if you didn't need it hollow, I suppose all of the interior shapes could be left inside.)

Thoughts:  If your vase is going to have handles, I would add them midway through the laminating process for attachment strength, and with wide bases at the joints.  Adding them to a basically finished vase would be difficult, and the joints would be weak.

The handles could be made from thick rope cut extra long, unraveled and splayed out at the ends to be attached to the PM.

If you planned on using a pulp for the last layer, you could probably use larger pieces for the lamination, even if they wrinkled.  It would be faster than many small pieces, and the wrinkles should be covered with the pulp and the pulp smoothed.  If you instead wanted the paper laminate to be the final coat before decoration, you would need to use smaller pieces to avoid wrinkles on the curves, which would be very hard to smooth out for a good finish.

I don't know your final use, but if it needs to be steady, weigh the inside of the bottom with small bags of sand.

Painting it with a few coats of a neutral-colored acrylic or latex house wall paint should give a good base for decorating.

I looked at Google Images for Grecian urns, and the general dimensions for the size you plan on doing would be about 60" tall x 35" wide.

There are large beach balls like this:  http://www.birthdayexpress.com/Inflatab … hwodVmKkiA

... but they are a summer-only item, and can be hard to find.  Keep in mind that when they say 48" they mean when the ball is flat.  So that is 2  48" flat circles (96" around the center), divided by 3.14, which would provide an INFLATED ball diameter of close to 30".  It takes far more material to cover than you would think likely.

Sue

You're always right, David!  You wife probably finds it intensely annoying.
:-) 

Sue