Hi,

If you are starting with pure  sodium alginate and using Ca2+ ions to cross-link the polysaccharide, you can change the kinetics of gel formation by using different sources of calcium.

This reference describes these effects:

http://www.sciencedirect.com/science/article/pii/S1878450X13000073

Good luck!

Dear Giuseppe E. Giammanco,

Thanks for your comment, It is inspiring for me. I red the article, you mentioned; however, I want this modification for molding process and this article is about spherification. the question is: how I can change the amount of the calcium salts to suit for my purpose. and how I should mix the alginate water and salt?

Best Regards,

Dear Saeed, 

You can add an extra ingredient to slow down formation of the Calcium-Alginate gel. As far as I know, trisodium Phosphate should have this retarding effect. This is what they do in the alginate-based products used for dental impressions, and they do have a window of time to work the material and put in in the mold before it sets. 

Best,

Dear Giuseppe E. Giammanco,

Thanks for your helpful comment. I have seen some commercial products which change their color during application for instance their color changes from white to pink when mixed with water and return to white after setting. do you know what reagent could add this property to pure sodium alginate??

Kind Regards,

You may possibly want to check also the following somewhat related discussions: https://www.researchgate.net/post/Does_change_in_pH_of_sodium_alginate_affect_final_encapsulated_cell_viability https://www.researchgate.net/post/How_can_I_make_alginate_disks_that_I_can_put_into_a_24-well_plate/1