About shrinkage

[felicity]

We were talking with halay about shrinkage and I decided to post our calculations and examples here just in case somebody's interested. Of course this is my understanding of the matter.

In felting shrinkage is the difference between size of wool you've laid and the size of the resulting piece of felt.
Example:
if you lay the wool at the template 100 cm and get a felted piece of 70 cm that your shrinkage is 30% (100-70)/100.

% of shrinkage is different depending on wool and how you do your felting. That's why you need to make a sample before you start important project. After you know the shrinkage you can calculate the size of template.

Example:
If you want to know how big template should be to get the size you need you do calculations backwards:
30% will shrink, 70% of the size of template will stay. 1/0.7 = 1.43 which means that to get the size needed you have to multiply it by 1.43 and this will be your template.
I usually use proportions.
Example:
You want a template for the 53 cm felt.
100cm --> 70 cm
Xcm --> 53 cm.
X=100*53/70=76cm. This is the size of template for 53 cm felt and 30% shrinkage.

I hope it's not too complicated...

[luvswool and dyestuff]

Felicity, I am very interested in shrinkage rates but have not yet had to deal with it, since I am in the learning stage. When I get ready to do "important" projects, this is definitely a calculation I wiil need to understand. Having not yet done many samples, I am not ready for the big projects. I seem to do okay with scarves and smaller items, but a large sculpture or vessel will require some math exercises. Thanks for posting your shrinkage calculations!

[Teri Berry]

Funny this should come up today, I spent a chunk of yesterday evening trying to set up an Excel spreadsheet that would calculate both shrinkage rate (I prefer to work with total area rather individual lengths) and what you starting size needs to be to achieve a predetermined size. I will attempt to attach it here (not sure if the forum accepts spreadsheets  ) - you are more than welcome to use it to your heart's content.


shrinkage calculator.xlsx (14.14 KB)

[Pandagirl]

Teri, you are a woman after my own heart. I make notes and calculate the shrinkage rates based on each project and how I roll, rub and full each one, but hadn't gotten around to making a chart. I can open the chart just fine. It may be helpful as you expand your experiments to note the type of wool, silk, weight, etc. not all wool and silk shrink the same. I dyed some china silk yesterday along with some silk gauze and both shrunk in the process as well. But not in the same way.  Thanks for the chart!

[felicity]

Thank you Teri! There is something in the air I suppose...

[Teri Berry]

Marilyn, it sounds like you are far more disciplined than me, I have a stack of about 30 sample squares that I still need to label up with what they are and their shrinkage rates.... There's just too many far more interesting things vying for my time 
At least the spreadsheet should speed up the calculations when I finally sit down to do them

[luvswool and dyestuff]

Very impressed by you ladies--calculations, spreadsheets and notes on techniques, shrinkage rates and materials! Phew!

[Shepherdess]

Felicity, great job explaining the calculations.

Your spread sheet worked for me Terry. I appreciate knowing people like you.

I am a bad note taker or very good at being precise. It's one of the things I like about felting I can usually make something shrink a little more or stretch it a little. I know if something is going to shrink 1/3(33%) my template has to be 50% bigger. If it will shrink by half(50%) it needs to be twice as big(100%, bigger). Its a good rule of thumb. I work it out for things like hats, vests and new projects but not for scarves. I know an 8 foot start length will work out right.

[liene]

shrinking % is always so tricky especialy when combining sveral types of fiber (tops and fleece for example. also it is very important when making the example/test felting piece to make it as thick as the project will be, thicknes - amount of layers is important

[halay]

Teri Berry, I have difficulties opening your shrinkage calculator.xlsx (perhaps my old computer does not recognise files with x in the end. I would agree with Liene in that you need to make a sample before you start a "serious" project considering the thickness, i.e. number of layers, therefore a single formula may not work but is a good orientation. This is such an important topic that it calls for writing and posting a tutorial. Felicity and/or Teri berry, would you be willing to write one?

[Pandagirl]

Halay, I think you have to have one of the newer versions of excel. Perhaps Teri can save it as an. Xls file and you'd be able to open it unless some functions would be lost.

I think a tutorial is a good idea, but definitely when working on new or unknown fibers a sample is the only way to go..

[felicity]

Very much agree with Marilyn! I wouldn't mind to write a tutorial but what exactly is needed? All my formulae above were about calculation a shrinkage starting with making a sample. There are so many points to consider:
- what kind of wool you use;
- how much of wool you use to make a sample of certain size. It may be number of layers (and everyone has their own thickness of layers!) for wool tops and just gramms for carded wool;
- direction of fibres;
- use (or not) of decorative fibres or fabrics for nuno-felting, which limit shrinking;
- the way you felt - if you just roll and rub gently shrinkage will be less than for agressive felting (bashing and hot-cold water treatment);
- texture you are after - smooth felt or textured pebbled finish;
And so on! I'm sure I've fogotten something...

[Pandagirl]

You're right Felicity there are so many variables!

[zed]

I have a section in my Wet Felting/Notebook cover tutorials that explains as simply as possible how to calculate the shrinkage when making a sample and how to use that info to increase your template/layout size.

I can edit it and email it to anyone who wants it?

[Shepherdess]

When I did boots we had to make a samples to the thickness we wanted the boots. Then no only calculate the shrinkage but calculate the weight of wool need for the project, using the square inches of the whole boot.