Originally Posted By: Ducked
Yeh, I thought it looked a bit coarse. Published accounts of this method (apart from the original "business card" version) tend to be a bit coy about the medium, but some appear to be using fine filter paper, others specifically refer to Thin Layer Chromatography, which usually implies a silica coating on a glass or metal slide.
Coarser media probably won't show structure or debris fields as well. I've only tried fine filter paper (which of course I've lost) and printer paper, both of which looked a bit finer than your picture but still weren't very convincing.
Dunno. You don't have much structure and it isn't very dark, which is good as far as it goes, but I don't much like the peripheral line irregular edge, though that could be the medium.
I used to have a few links to reference pictures (which you've probably got anyway) but this is the only one I could now find from a quick look.
http://www.magna-guard.com/OneDrop.html
For WIW (not much) the one that looks most like your picture (to me) says "plan to change"
Anyway, to answer your question, of course you can. Who's going to stop you?
If you're going to continue to blotter test as an early warning of awfulness, you should perhaps try and get, and test, some finer media.
The idea of coarse/fine medium sounds interesting and pertinent in quality of Blotter Spots .....
and would give it a try to assess its difference in Blotter Spot test results in times to come.
Basing on the link provided, I would agree with you the presence of irregular peripheral edge (being related to oxidation ring??) would lead one to the recommendation of 'plan to change'.
Oxidation, if any and there should be one, appears to be insignificant and inconsequential as there is total absence of 'centre zone' in the blotter spot , as you'd rightly pointed out that there is not much structure and it's not dark but light gray ........ and referrencing the following links:
http://www.machinerylubrication.com/Read/29353/evaluating-lubricant-dispersancy
http://media.noria.com/sites/archive_images/backup_200307_blotter-tab1-2.gif
...hence my question of proposed extention of OCI of say, 8500 miles subject to satisfactory Blotter Spot Test results.