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Lynn Javoroski
Senior Member
Username: lynn_javoroski
Post Number: 146
Registered: 07-2002
Posted on Tuesday, September 07, 2004 - 02:37 pm: Does anyone have an explanation of the difference - if there is one - between a satin finish and a brushed finish on metals? Is it a degree of shine (or lack thereof)? is it a base metal difference (aluminum is brushed while steel is satin)? I see these two terms used seemingly interchangeably. But surely there is a difference?
Ronald L. Geren, RA, CSI, CCS, CCCA
Senior Member
Username: specman
Post Number: 56
Registered: 03-2003
Posted on Tuesday, September 07, 2004 - 03:08 pm: I've always considered them different.
A satin finish, usually a mill finish, is one that is not polished (i.e. degree of shine, as you stated). Whereas a brushed finish is a mechanical finish applied to the metal which can be directional or nondirectional. However, you can have both (i.e. brushed, satin finish: No. 6 for stainless steel).
Refer to ASTM A 480 for specifics on stainless steel, and the Aluminum Association (I think this is AA DAF-45) for aluminum finishes.
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 306
Registered: 10-2002
Posted on Tuesday, September 07, 2004 - 03:23 pm: One of my favorite topics!
NAAMM (and in addition ASTM A480 for stainless steel) has specific standards for metal finishes. If we look at just the mechanical finish and not the coatings (anodic, chemical and otherwise) the finish designations and the names for those designations for both aluminum and the copper alloys are the same.
Stainless steel has a totally different designation, and only the numbers, NOT the names are official.
The Aluminum and copper alloy finishes have many more varieties defined in the standard. These include 3 kinds of satin, and in addition, brushed is also an official designation for these metals. M31 = Fine Satin, M32 = Medium Satin, M33 = Coarse Satin, M35 = brushed (there are many more). Of these 4 examples, only M32, Medium Satin is considered a commonly available finish. The others are items that are often not available in prefinished sheets, someone has to do it custom.
Which means also that technically, 'satin' for aluminum and copper alloy materials is not a valid term. You have to ask for the kind of satin you want. If you make no distinction, you get Medium Satin.
Stainless steel has only a few finish designation - and important note, NONE OF THEM HAVE OFFICIAL NAMES.
The most common architectural stanless steel finishes are 4, 6 and 8.
4 is what people typically refer to as 'brushed'. However, its official description is "A general purpose bright polished finish..." In different regions (and for different manufacturers) around the country this is called brushed stainlesss, satin stainless, directional polished finish as the most common names. But, using the name at all is cause for problems if you don't define it with a NAAMM number.
Number 6 is defined as "A soft satin finish having lower reflectivity than the number 4 finish..." It would be more correct to call this satin, and the use of this term by fabricators is more common in many regions. But again, no official term.
Number 8 is "The most reflective finish commonly produced..." Some call this reflective or specular, or mirror polished or in some cases, simply polished.
There are many fabricators that will create special finishes, etched, etc. None of those have official designations other than manufacturer's product numbers. So if you were in the habit of stating etched stainless and give nothing more in your spec, well, the degree of etch and the manner in which it is done is up to whoever wants to do it - unless you have a control sample that you require them to match.
To give you the exact definition of Number 4 from NAAMM, it is "A general purpose bright polished finish obtained by finishing with a 120-150 mesh abrasive following initial grinding with coarser abrasives." ASTM 480 goes into more detail about the depth of the cut, etc, but you get the drift, its a technical description.
M32 in aluminum and copper alloys is much less specific stating only "These finishes are produced by wheel or belt polishing with grits of varying degrees of fineness." Wow, that's specific, eh?
Overall, ASTM has more definition in how to produce the stainless steel finishes than the NAAMM standard that I happen to have handy, but still its a description of the finish, no official name to the finish is given.
Obtain samples that are good representations of the finish, have everything match the samples.
William
Richard L Matteo
Senior Member
Username: rlmat
Post Number: 60
Registered: 10-2003
Posted on Tuesday, September 07, 2004 - 04:18 pm: William, Thank you for giving the correct information. However, one minor point on #8 stainless steel finish - according to what I have been told by the stainless people, #8 is still not really a true mirror polish. You will still some small degree of striation, this goes for "super 8" as well. If you want to receive a true mirror polished finished, it should be specified as "mirror polish". This is the only exception to the stainless number designations.
The same tends to hold true for polished bronze (muntz metal) finishes as well.
I used to specify a lot of stainless steel & bronze and it was the only way we could get the finish we were looking for. Also, I reinforce your recommendation to obtain samples - it saves a lot of hassle later.
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues
Post Number: 307
Registered: 10-2002
Posted on Tuesday, September 07, 2004 - 04:34 pm: Technically that is not correct, though one could quibble with the standard. It states that it is 'essentially free of grit lines...', and that is why even specifying the NAAMM designations (or ASTM 480) its best advised to add '...as required to match the Architect's sample'. Then you get the sample of the quality you require.
I have seen some number 8 that look like a bad 7. 7 says its reflective except that it adds that 'but "grit" ines are not remved.' That coupled with the way 8 reads, one should expect no lines in 8. Your sample sets the tone on that. I do that, I get what I want, up to the point that they start to throw money at the Owner and some will take small dollars to 'not notice the lines.' But on any quality job, I have no problem getting what I want with a requirement to match the sample.
The same is basically true for the aluminum/copper alloy NAAMM standard. You can get it as a true mirror with the M21 smooth specular finish...but you need a control sample to get it.
Specifying 'mirror', that does nothing for you without a sample. Some mirrors are foggy, you will still get a lot of Number 7 stainless steel sent to you.
But I think on some things like this, it depends on the region. Some major metropolitan regions that use a lot of really mirror reflective finishes, you get it like I do here in DC. But some other areas, you might have to go to greater 'verbal lengths' to get it. And even then, samples are required to actually demonstrate what you want.
William
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