Thickness after Back coating.

[chesscuber98]

The thickness of a paper really confuses me. Suppose a sheet of tissue paper (25 gsm) is backcoated with another sheet of tissue, does the paper thickness stack up to make a sheet of 50gsm? If so how come Double Tissue is much thinner than a readymade 50 gsm paper? Also How thick does Tissue foil become?

[origami_8]

You are mixing up two things here: Thickness and Weight.
Gsm is Grams per Square Meter it tells you the weight of the paper. You could measure it yourself by putting one square meter of paper (one A0 sheet or two A2 sheets, or 4 A3 sheets or 8 A4 sheets...) onto a scale.
the weight doesn't necessarily tell anything about the thickness. Lokta for example is pretty lightweight with usually about 40gsm but is rather thick whereas tracing paper ranges usually in the 120gsm area but is very thin.
To measure the thickness of a sheet you need other measuring tools like for example a caliper. The problem here is that especially on handmade papers the thickness may vary significantly throughout the sheet.
So if you want to determine the weight of Double Tissue or Tissue Foil, put it on a scale. If you want to determine the thickness use a caliper.
To your question whether the thickness/weight adds up, of course it does and glue and foil add thickness and weight too. Still those papers are very thin, strong, crisp and good for complex models.

[chesscuber98]

Thanks for clarifying. That certainly does clear things up. After some searching I realised that gsm is density. Thank you.

[origami_8]

Not quite. For density you would need to know the thickness of the paper too as density is the weight per volume and not per area. A square meter is only the area or in other words 1m x 1m = 1m² to get the volume you need to add the height like for example a cubic meter = 1m x 1m x1m = 1m³.
So gsm tells you the weight of 1m² independent of its height.
To make things even more complicated neither weight, nor thickness nor density are reliable aspects to tell whether or not a paper is suitable for Origami. Many more factors play a role here like for example lengths and strength of the fibres used, how they are arranged in the paper (all in the same direction like on machine made paper is weaker than random directions like on handmade paper), how much sizing (internal glue) the paper has and many many more.

[chesscuber98]

For the first part, yes that is true, but in the case of paper manufacture, it is considered as weight per unit area. Source:
http://en.wikipedia.org/wiki/Paper_density

For the second part: I totally agree with you there, what makes it even worse is that a paper that wont work for one model may work for another.

[origami_8]

Very interesting. I wonder if that is really true or if someone just confused something here and everyone believed it because Wikipedia says so. It's the first time I heard that paper manufactures misuse the term density in this way. All the other language articles are basically called Grammage what seems more plausible to me. I'll try to find out whether there are some references that back this use of "Paper density" up or if someone just tried to write an article about a subject he had no idea about.

Edit: I've found an article that sums all the properties of paper nice up and clearly shows the difference between grammage and density: http://www.ipst.gatech.edu/faculty/raga ... istics.pdf

[chesscuber98]

I have never thought wikipedia to be so misleading. Thanks for the clarification.

[Benlewisorigami]

well are you asking if the thickness of the paper changes? Because the thickness doesn't change. At least for me. The weight becomes heavier because you are adding something to the paper. Take unryu for example. Mine is SUPER light and thin.. almost like a cloth, but when I add mc to it, it becomes heaver. The thickness doesn't change, only the weight.

[origami_8]

@chesscuber98: The good and the bad thing about Wikipedia is that anyone can write and edit articles there. Good because that way anyone who has knowledge about something can share it with the world making up for one of the most detailed Encyclopaedias out there. Bad because not everything you read there necessarily has to be true. I've read through the history of this article mentioned above and found that someone seems to have written this article in the past thinking Paper density would be the same as Grammage. Later on someone added that this would be used by paper manufactures without stating a source backing this up. Later on people just seemed to believe what was written there and no one complained. A short search on the internet showed me that paper manufactures would prefer the term basis weight in the US or grammage outside of the US. Where basis weight is actually the weight of a ream (a specific amount -often 500 sheets- of the basis size a paper is produced in) in lbs. All the more serious sources seemed to agree on that and on the fact that volume is just as defined weight per volume.

@Benlewisorigami: I'd guess it depends on the structure of the paper, how porous and dense the paper is whether the MC adds to the thickness or not or maybe even reduces it. But without accurately measuring it you wont know for sure.