Science Buddies: "Ask an Expert"

HI!!
I'm investigating the effectiveness of sunscreen spfs by using photopaper
Here is my method
Aim
To determine whether there is a difference in the protection against UV rays by sunscreens of different SPFs 15+, 30+ and 40+.

Hypothesis
There won't be a significant difference with the protection given by sunscreens with higher SPF to those with lower.

Equipment

-9 pieces of photo paper
-1 bottle of photogenic fixer (sodium thiosfulate)
-1 A4 sized plastic rectangular container

Method
1. Cut the photo paper vertically into 3 equal sheets of paper and label the sunprint paper from 1 to 3 to indicate the SPFs
2. Squeeze a small amount (size of a 50 cent coin) of sunscreen with SPF 15+ on the centre of the glossy side of the phot paper and spread the sunscreen equally around the paper
3. Repeat steps 1-2 with SPF 15+ and 45+ on the remaining 2 sunprint paper
4. Place the 3 sheets of paper carefully into the plastic folders and leave it outside in a sunny area
5. Start the timer for 5 minutes
6. Place 200mls of Photogenic fixer into the Rectangular container in a dimly lit room
7. Bring the folder back into after 5 minutes
8. Place the photo paper glossy side down for 3 seconds in the photogenic fixer and then rinse immediately with cold water
9. Lay it to dry for fifteen minutes
10. Scan the three solutions onto the computer
11. Analyse each one by determining the blue pixel value to get an average darkness for each sunscreen and time interval and compare the data
12. Repeat steps 1-16 twice leaving the folder outside for 10 minutes the first repeat, and 20 minutes for the second repeat

Originally, i was going to use sunprint paper but i couldn't find any stores selling it in Australia, and if i had to get it overseas, it may take too long. By the way, i took this off a couple of very similar experiments, and one said you could use a fixer- but it did not specify what type of fixer. Another source recieved sodium thiosulfate from her science teacher, and i can't do that in my case. Secondly, i need 'photo paper' according to other sources it said developing paper-is developing paper dark room black and white paper or the ordinary white glossy photo paper used at home?

Please help
p.s. if you know anyone in america who could send sunprint it would be nice to tell
p.p.s please reply soon
thnx
Avatarbelbel

I suspect that your proposed methodology has several flaws:
1) the chemicals in sunscreen may affect the photo sensitivity of the photo paper
2) the chemicals in sunscreen may affect the development process of the photo paper
3) the photo paper may not be sensitive to the UV spectrum
4) the photo paper sensitivity to visible light may swamp the UV spectrum exposure

That is just for starters.

It is very good that you are thinking about your procedure and how you will analyze the results before doing the experiment. You have asked detailed questions and your procedure is a very good start. Unfortunately, if your project is actually due on the 5th, I don't think you will be able to do this experiment and do a good job on it. I agree with Craig in that you would need to use paper that is sensitive to UV light. I think regular photography developing paper is sensitive to light in general, not just UV light. I did find some UV paper strip indicators, but you would have to order them probably, and then you'd hardly have time to do this experiment. (paper strips: http://www.uvprocess.com/products/CURIN ... BL%20B.ASP)

We do have a project about this exact topic, but it requires you to order a device, and I don't think you'd get it in time. Here it is for reference: https://www.sciencebuddies.org/science- ... p015.shtml

In the future, it is very important to make sure your procedure is going to work well ahead of time. It sounds like you were thinking about this, as you posted on the forum (so that is very good!), but even still, you should have thought about it even earlier. We all make mistakes, you just have to learn from them and do better next time.

But, with that negativity out of the way, don't despair! There are many projects on Science Buddies you can do quickly and get a good grade.

You can either take our Topic Selection Wizard for some topic suggestions (make sure to say that you have less than a week until the project is due), or you can browse our project ideas. Both of these resources can be found here:
https://www.sciencebuddies.org/science- ... deas.shtml

Let us know if you have more questions! Good luck!