Chemistry (including Biochemistry)/Lye soap



I've been using lye based soap to wash my laundry.  However after a couple of months I noticed my whites had a green hue to it.
In the other hand washing with lye in a plastic bowl and soaking the laundry over night never gave me the green hue for years. It only happened when I started using it in the washing machine.  Could metal tub be the issue?
I have soft water and a filter is installed.


ANSWER: Hello! Sorry about the lateness of this reply.

Lye is a common name for sodium and/or potassium hydroxide. This solution is a strong base. Strong bases like lye are very good at dissolving greasy things and are often used to get clothes very clean. It makes sense to add them to soaps.

However, what is a strong base? In simple terms, chemists refer to a base as strong when its two component parts split up completely in solution. This makes them very reactive with anything else they encounter. In day-to-day life terms for most people, a strong acid or base is dangerously caustic and can dissolve metals... or you. (Hence all the warnings not to eat lye or put it on your skin.)

So you're 100% correct that the metal tub is the issue. Please stop using lye based soap in your clothes washing machine. While I'm not certain exactly what the lye is dissolving (a green hue may be copper or nickel metals) I *am* certain it is damaging your washer. This cannot be good for the lifetime of your machine and may result in you needing the plastic bowl method all of the time.

Cheers and good luck!

---------- FOLLOW-UP ----------


Thank you for your informative reply.

I do have have copper pipes and a water softener system.
The normal detergents never gave the green hue. It's only the lye based soap when in contact with metal. Because I turned the washer on and took the water from it and filled a plastic bucket and washed the clothes, and no green hue showed in the clothes. The reason I did this is I was trying to know where exactly is the issue.
And it turned out to be metal.
But I read lye isn't present in the final product after it gets mixed with the oil to create soap.
And at the end again I am still puzzled.



It is true that soaps are made by mixing lye with oil. Lye is really inexpensive to make chemically, while oils have to be pulled from the ground or isolated from plants or animals, making them more expensive. Often in industrial reactions extra helpings of the cheap stuff are used to make sure all the expensive ingredient is used. Long story short, there may be just a little extra lye in your soap left over from the initial reaction process, which then goes on to tint your clothes. :)

If you had access to a couple samples of soap, it might be interesting to see if different brands produced differing color levels. :)

I just had a thought. You could try adding ~100ml of white vinegar or a small amount of citric acid to your washing machine in the basin when you use the lye soap. If the tint is truly caused by excess lye, then the vinegar ought to neutralize the extra base and protect your machine. (i.e. the tint should vanish.)

A couple interesting articles to help clarify things (I hope) (Says here lye reacts with galvanized zinc, which is a popular metal coating.)

This looks legit chemically, and the other soapmaking articles are interesting.


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Trista Robichaud, PhD


No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.


I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.

2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association

Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)

Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011

Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present

Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011

Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)

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