(click picture to enlarge)
I was thinking of just taking some video of me ironing...it's near impossible to explain something like this - it just comes from lots and lots of practice.
Forget timing yourself, forget reading manufacturer's instructions. You have to eye it and feel it out.
I can only offer a few pointers...although rather detailed, you still have to feel it out.
1) Always start at one end, working one ironing sheet at a time. Choose carefully which sections you iron and in what order you iron them. Consider everything you know already about how the beads curl and contract when deciding this. Iron each section well and forget about consistancy - it's near impossible to iron a large sprite evenly the way you can with small ones.
2) Once you iron the first section, wait until the ironing paper removes itself on its own accord. Don't pull it up or any beads near the edges that haven't fully fused will pull out of place. Once you can safely remove the sheet, find the beads along the edges that have undoubtedly lifted from the pegboard - press these back down into place. Some smaller sections of beads will break from their original fusing. Don't fret. You are, in a matter of speaking, distributing thesee portions in the space between what has been ironed and what has yet to be ironed. Once you have these portions pressed back into their approximate positions, place your ironing sheet over your next section, being sure the paper overlaps a good portion of the previously ironed section, including those portions you re-distributed.
3) Iron your next section, beginning with the very edge that was created from the previous section ironed. Once these portions appear to be fused properly, move on to the rest of that section. Repeat steps 2 and 3 until you are finished, then move on to step 4. However, consider the following:
As you get further along in your large sprite, you need to do one of two things: 1) remove pegboards from 2-3 previous sections ironed or 2) place large flat objects on top of the aforementioned sections (college textbooks work great!). The reason for this is, as you probably know, the sprite contracts. This is inevitable. Heat melts and expands while cold solidifies and contracts. This wouldn't be a problem except for the fact that your sprite has many holes, still occupied by pegs on the board. They begin to tug on the sprite, pulling on it in all manner of unwantedness (not proper english, but necessary to convey this principle). So, as stated, you need to either remove the problem (literally removing the pegboards), or counteract it (create opposing force...like heavy, lengthly, otherwise useless educational material).
4) Once you have finished ironing all of the sprite, wait until it cools just enough so you don't burn yourself. Remove all pegboards one at a time from the bottom, keeping the sprite relatively flat and level. Once you do this, let it sit. At this point you do not need to place books on top to keep it flat unless it is curling a lot but, as stated, still being on the pegboards is what causes it to curl most, so since you removed the pegboards, this should not be necessary. Plus, you will iron the other side, so it will be heated and become relatively floppy again, allowing you to correct its 'posture' once more.
5) Once it has cooled enough to become relatively stiff, carefully flip it over. Do not wait too long or it will be too stiff and may break under its own weight and size. Then iron the backside in sections, this time placing Calculus, Physics and History on top of each section as you go along. Also, make sure you are working on a large flat surface, or your front side will become uneven, as it will also heat up and take to the shape of anything below it. Once you finish your final section, place Biology on top and let it sit for a good hour. If you want, for the sake of perfectionists-like-me, use a large flat object in between the Bead Sprite and the books, for more consistancy.
Etc) Feel free to iron the back like there is no tomorrow - only be sure to iron it somewhat evenly if you intend to mount or convert the Bead Sprite into something useful, like a giant magnet or placement, what-have you. You will notice over time that the more you iron the back and the more the front heats up via transfered heat through the sprite, the flatter the front will be - however, I have experience dimples in the front of some sprites due to a crumb on the table or overheating (whereby a melted bead on the front side heats up so much, the layer of plastic that initially melted over a hole becomes too thin and breaks, leaving a hole).
Well, there are my personal tips for ironing big-ass-mother-fuckin-sprites (pardon my french, but is there any better name for em?).