Classify, Classify

Hi Everyone, question about classifying. I am in the process of getting classifying screens. What do the numbers mean ? I am looking into classifying Small stuff. Possibly 50, 100, 150 mesh screens.?  Numbers I see are marked 1/4, 1/8, even 1/50. Have also seen decimal numbers such as .50, .25 etc which I assume are quarter,half etc.... some instances show a negative in front of a number ( -50, -100 ) Have also heard them refered to as # 8, # 10 etc...So, I realize it all relative somehow  but, what do I look for in the numbers. is a -50 the same as a 1/50 ? Any help to understand is greatly appreciated. New to this site and have learned some things. Thank you for your time

Ric s.

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  • Thanks for the great info everyone.  I thinkin I going to start with 1/8 and a 50 for now. I'm sure more will be added as Things go along and I finger it out. Besides nuggets, pickers , and visible gold ( obviously ) I am after the fines and flour  stuff that can be seen without squinting too hard. I am sure I will have many more questions as things begin moving along.  Thanks again  ric s

    PS.  That video doc did about hydraulic equivalence is very educational

    • My first screen was a #12. I've been at it for a little over 2 months 2 days a week every week.
      I pan, re-pan, pan again, and then pan again till I am confident I have it all.
      I decided recently to purchase a #50 and when I got it in the mail I saw that much of my stuff is +50 or even + 30. I still do get lotsa -50,-70,-100,-150,-200 but I was surprised that, once "measured", the stuff I was finding was bigger than a #50 screen. So it was cool to learn reference points and to see the equipment you need is determined by what you are looking for. The next thing I'm gonna get is a #20 and see if that splits the difference favorably.
      Also I have saved a lot of my cons so this winter I'm sure I'll go thru all that with my #50.
      • sieves or classifier screens are kind of like lays potato chips..... you cant have just one ;-) 

        One the Clearwater river here in north central idaho, my biggest share of beach sand is minus 30 to plus 70,  what i eventually found by purchasing a 20, 30, 40, 50, 60 and 70 screen was the bulk was either plus 40 or plus 60  depending on the beach, the eddy, or how far out in the river i dig in low water [farther out the bigger the particles]

        But size does determine the piece of recovery equipment best suited for more volume thruput as to what will fall out.  Ive used small scale equipment that a trowel was maximum per minute all the way up to a 2 ton plus per hour reverse helix machine [old tri-R, now Oro-Industries] and with each type of machine you still use a classifier to extract maximum metal from the aggregate in one or another!

        At the end of the day, we all want 2 things, more gold and to have had a excellent time in the outdoors.... [what you thought i was gonna say a cold beer and hot.... this a mining discussion;-) ]



  • The smaller the number the larger the holes are and less per inch of screen, ergo a #2 screen has 2 holes per inch and is commonly called a half inch classsifier.  The larger the number the greater number of holes but are smaller openings, ergo #100 is 100 openings per inch and is commonly refered to as a 100 mesh screen which will allows that which is under that size to fall thru which is then referred to minus 100 or expressed as -100. 

    It takes a decent set of screens to be able to utilize them to their best potential, I reccomend to the folks I sell to if they are just prospecting a hole to use a #2 to shovel into their pan as it is unlikely they will hit a larger than 1/2 inch nugget where they test shovel [it does happen].  For the serious descretion a person needs to start with a #8 or 1/8 inch classifier where everything bigger is easily panned or scanned with a metal detector and sorted fairly fast..... then drop down in size to the closest number doubled, ergo double 8 to 16, and we have bucket classifiers in 12 or 20, and depending on the cobble you are classifying, you may want to go with the 12 but for the most part the 20 is good enough and again everything that stays is easy enough to pan.  from 20 we end up jumping either to a 30 or 50 in bucket classifiers which the "double 20" falls between, however most beach sands will require both screens and the bulk of what is found falls in that category.  The next set that are available is the 70 mesh and 100 mesh screens [#70 & #100] and again its up to the end user as what volume of fines they want to deal with and where the size of the micro fine gold lays at, but when you have minus 50 to plus 100 [that which didnt fall thru the #100 screen] the smaller gold doesnt stay in the pan as easy when you wash it all together.... ergo 50 mesh sand can be every bit heavy as 100 mesh gold and move it around enough to be lost and you wish for more sizes.

    the brass [and now stainless] 8 inch [also the older 3 inch, 6 inch, and newer 12 inch] tyler equivalent test sieves [ ] are stackable into each other for adding to a shaker [search for ro-tap sieve shaker for reference] come in a variety of # and there have been several makers of the sieves but they all seem to fit each other when put together.... I personally have sieves from #4 to #325 and yes have recovered gold from the 325 which is so fine when dry [the only way to be able to get it to pass thru] that when pulled apart it literally floats.... from a five gallon bucket i can expect to recover about a tablespoon of dust maybe 2 tablespoons and out of that there will be a a smile of gold visible to the naked eye once in the pan and under water separation.... air drying takes way to long for most people to test.  And no, these are not inexpensive but are well worth the cost if you need to do a larger volume of testing of a claim be it a placer or a when you crush out a lode. 

    Classifiers are, in my personal opinion, a very necessary part of any miners full kit of equipment if they intend to be serious about what is going to pay out and what the optimum equipment to be used will be....

    I hope I havent added to much to the confusion, and I hope that if you have more questions you ask!!

    My computer froze up last night while typing and i had to redo my thoughts.



  • As I understand anything that falls thru a #50 mesh is -50. If it also falls thru #100 then it's -100 and would be REFERRED to as -100, not -50 even though it fell thru 1/2 inch all the way thru #50 and #100.

    As far as what the # thing is, it's how many holes are present in the screen for the length of an inch.
    So a #12 has 12 linear openings (holes) per inch, 144 holes per square inch.

    Edited: already answered:)
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