Hi Joe,
I have a couple of thoughts on this, first I will tell you how I pretreat.
First I lightly mist the area with distilled water just so you see a slight beading of the water, very light.
Then I spray my pretreatement just so I see a slight whiteness of the liquid.
I then use a boar bristle brush and brush down fairly firm to make sure to get it into the fibers. I only brush the one direction.
Then I use the quilan parchment paper and press at 330 for 15 seconds
Then I remove the paper and press another 5 to 10 seconds until I dont see any steam coming off.
Now my 2 thoughts are either the pretreatment may be too heavy or the white ink layer may be too heavy.
Have you thought about trying to print 2 passes at 720 x 720 or printing white at 1440 x 720?
I learned the misting of distilled water from one of the users that used to post here that was one of the original printers of these machines and it works really great as it makes sure you dont get that box look from your pretreatment, totally gets rid of that and in my opinion seems to make the pretreatment mesh better with the fabric for some reason. Hope this helps some Joe, hopefully I mentioned something you can try
