Problems with ColorfabbXT
I have had my Mk2 for about a year now, have had it working perfectly on standard PLA material, But I recently got and tried some ColorfabbXT , and seem to have major problems. I use a Buildtak bed, glued to the top of the original Prusa bed, and this has worked fine for PLA, ABS and several other materials. I had noted other comments that adhesion was poor with XT, but on the Buildtak it seemed fine for me. The problems show up as either rough surface on fully filled layers, or really bad blobbing on layers with infill. See photo. This is with standard 0.4 mm nozzle, extrusion multiplier set to 1.0, extruder temp 240, bed 90 on first layer, then 65 on upper layers. Filament measured at 1.75 mm, and set to that in the slicer. 
?dl=0
Any comments would be appreciated.
Re: Problems with ColorfabbXT
Have you seen Eastman's Amphora 3D Polymer Consumer Selector Guide document? It is gold with regard to filament made with Eastman's copolyester compounds.
I spent an hour or two getting my Simply3D profile converted from PLA to work with ColorFabb nGen (you have to read all the comments, as some of the advice is hidden there). I was rewarded by a near-perfect print first time out, and tweaking beyond that was extremely minor ... They do recommend no fan till layer 4, then 60%. I've gone to stepping it up gradually to 60% by layer 10 ... otherwise there is a visible shift in print "translucence" (some ephemeral quality of what the print looks like) if you go directly from 0% to 60% fan.
I initially retrieved this document on 5/18/2017 and recently checked on 5/9/2018 and the recommendations have not changed ...
ColorFabb XT is made from Eastman's Amphora AM1800 while ColorFabb nGen is from Eastman's Amphora AM3300 and ColorFabb HT is from Eastman's Amphora HT5300.
Link: https://www.eastman.com/Literature_Center/S/SPMBS4044.pdf
I hope this helps!
-- Clint Goss