I regularly use the pH pencil. It is what is known as a "Litmus Pencil."
I have had inconsistant readings with the pens as the tips have a tendancy to retain paper fibers from the frequent checking. The Litmus Pencis I have found to be extremely helpful in shops that call me in when combatting calcium carbonate issues or premature plate ware / plate blinding issues.
The pencil can also help in identifying problematic stocks that might contribute to delayed drying of inks because of extreme acidity or extreme alkalinity content.
Just this week using an imported cheap bond i had issues with oxidisation that i believe was related to paper ph.. every time i stopped on a changeover the plates showed spotting etc, to the point where i gummed the plates when stopping to avoid wasteage.. it did not happen on the coated stock i was running beforehand or the different coated stock i used on the job after.. my assumption was that the acidity of the paper was affecting the ability of the fountain solution to correctly protect the plate surface?? am i correct??
Based on what you experienced, it sounds as though the stock's pH was certainly out of the neutral range.
It's rare that you encounter an offset sheet that has an ecessively acidic pH but more so Alkaline. Typical printing stocks vary in pH from 6 - 7.5 pH. What you were seeing was probably the calcium carbonate being leached out of the sheet, attaching itself to the blanket, and between blanket and plate contact - it creates either sensitivity or in longer runs it can buff away the plate surface.
The calcium carbonate is used a filler and brightener in the manufacturing of offset stocks.
The coated sheet you ran was probably in the neutral range.
Take a look at this article from Sappi Paper about the effects of calcium carbonate when printing.
Best Regards,
Aaron Sures
Gracol 7 Expert
Pressroom Specialist
Gans Ink & Supply Company
(323) 867 -3677 Direct Cellular
Thank you Aaron... that is pretty much spot on to what we experienced... fortunately it was only 100,000 impressions, so only one shift of headaches We are having some issues with calcium build up on the edges of our rollers tho, going to a full size sheet on the press creates watering issues about 2" in from the edge of image, requiring some adjustment of profiles to keep a solid at 100 percent... its irritating but you work around it, and quite possibly only a new set of rollers will completely fix it, as calcium and lime rinses seem to be a short term solution only..
Something that has really worked for me in the field when encountering calcium carbonate issues / stripping issues of the roller train is the good ol' fashioned Copperizing Solution. If you have any copper rollers in the ink train, the calcium carbonate will leach itself to the rubber inkers and throw off the ink / water balance by making your rollers Hydrophilic (Water Loving) instead of Oleophilic (Ink/Oil Receptive).
The copperizing solution wil make all rollers within the ink train ink receptive and reduce the flooding on the edges as mentioned. Calcium fixes are good but they're just not the same - especially if you have tarnish on the coppers that are forcing the press operator to walk the tight ink / water rope. Bad rollers certainly don't help but if you have play in the water forms and ink form stripes, the rest is down hill.
I'm assuming that you run Komori's by your name? GAZ L 4 40?
Hope this advice helps.
Best Regards,
Aaron Sures
Gracol 7 Expert
Pressroom Specialist
Gans Ink & Supply Company
(323) 867 -3677 Direct Cellular
Yeah we have a handfull of komori's and some smaller heidelbergs... I have noted some discolouration on the copper rollers, especially the rider in the dampening systems of the 2 most affected units (cyan/magenta) on the 40" i run... all rollers are in reasonable condition and set correctly, when our local roller supplier next drops in i will see if they supply a copperization solution...
1 Chop the red cabbage up with a sharp knife.
2 Crush it with a "pestle and mortar" OR put it in a food mixer and grind it.
3 Add a very small amount of water.
4 Decant the blue liquid (pour the liquid into a clean glass).
5 Soak some blotting paper in the blue liquid.
6 Let the blotting paper dry out.
7 Cut the blue papers into small squares.
8 If you add a little bit of vinegar instead of the water, you will end up with red litmus.
ok i just bought a ph marker and apparently everything is normal, the paper is at 7PH, im not having any problems right now with the printing but a couple of months ago i had a problem with tinting, i change the fountain solution, the inks everything but the paper, im pretty sure it has something to do with the water/ink/paper ph balance, im i right?
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PH on paper
We are having some issues with calcium build up on the edges of our rollers tho, going to a full size sheet on the press creates watering issues about 2" in from the edge of image, requiring some adjustment of profiles to keep a solid at 100 percent... its irritating but you work around it, and quite possibly only a new set of rollers will completely fix it, as calcium and lime rinses seem to be a short term solution only..
